I guess tlop5 looking like the next buy

Okayyy, before we realize how Vijay has such a huge fan base in Kerala, you need to know about a trend that took place post 1990s.
Until the 1990s, Malayalees rarely watched Tamil movies and rarely Tamil movies got released in Kerala. Tamil Cinema prior to mid-1980s had a different movie culture. A very large percentage of its movies were based on Dravidian Nationalism. Whilst Dravidian Nationalism and Kerala’s Renaissance were similar in nature as both were deep-rooted in socialist values of egalitarianism, rejection of orthodoxy, etc.. Tamil Dravidian stories as such were irrelevant in Kerala because it was deeply rooted with Tamil myths as opposed to Kerala's milieu. You can asses it, watching some of the MGR's flicks. It shouldn't come as a surprise when Five CMs from Dravidian parties were actively involved in cinema either as actors or writers.
Sivaji Ganesan's 1952 Film \"Parasakthi\" was a 175 day theatrical run BO hit that made radical comments against caste system and glorified Dravidian Movement.
However, late 1980s saw several newcomers in the Tamil industry, particularly the rise of trio directors- Balu Mahendra, Bharathiraja and K.Bhagyaraj. They changed the narrative styles of Tamil cinema by the late 1980s. Instead of many traditional rural and Dravidian themes, newer concepts like college based love stories, urban-themed subjects and subjects relevant to middle-class society started coming up. And some of them like Balu Mahendra was a popular filmmaker in Malayalam too. Thus he knew Malayalee sensibilities well.
This was the beginning of the amalgamation of Tamil movies into the Kerala society.
Movies like "Moondram Pirai" was welcomed grandly in Kerala because of it's universal theme but Malayalam industry wasn't affected as much because late 1980s and early 1990s was a golden age of Malayalam cinema. We were met with revolutionary directors, actors, stories, film techniques etc. However, it didn't last long when Malayalam industry started facing stagnation period which would dominate it from late 90s until the mid 2000s. That's why Appuppan and The Boys have perpetual content.
Anyway at the same time, Tamil cinema got a second major boost, post 1992 there was a rise of superhero-centric movies or city-centric movies. In this period more directors like K.S Ravi Kumar, Mani Ratnam, Shankar etc came up and double boosted the Tamil cinema with their extra-ordinary movies. Movies like Roja, Bombay, Baasha, Padayappa had pan Indian appeal and was accepted well in Kerala.
Mani Ratnam's 1995 film \"Bombay\" tells an urban inter-religious human relationship against the backdrop of religious tensions between Hindu and Muslim communities.
Now, Why does this matter? Because Vijay, Surya, Allu or any non-malayalee actor for that matter, gaining clout in Kerala soil had it's bridge being setup much before their birth and is neither a result of their own nor something that happened out of the blue.
Before dwelling on the specifics of Vijay/Allu stardom, there are a couple of reasons that pulled Malayalees to Tamil movies. Lets analyse them

1. Songs:

Malayalam industry hardly had any variety apart from melodious songs which was well rooted in Classical and semi-classical notes strictly following the 'ragas' conduct. We did not have much fast dance numbers or the ones that could be played during a fest etc. It was hard for the majority of Malayalee composers to think something not traditional. And our youngsters were frustrated from being unable to release their pent up energy.
That is when our Magnus Opus A.R Rahman attracted youngsters with songs like Chikku bukku Rayile, Telephone Manipol, Mukkala Mukkabla, Gemini Gemini, etc from Tamil Industry. Our dhaaridhrayam for songs were so bad that we celebrated songs of absolute nonsensical movies. Jassie Gift was our only bragging right back then. Nillu Nillu Ente Neelakuyile, Themma Themmadi kaate being some of them. Other medium, where youngsters took solace in their teenage years were in Malayalam Album songs.
Even today, we lack good fast paced songs that is simple for every tongue to sing because our lyrics are too complex. For example, Thallumaala featured many songs that's tough on a foreign tongue, Kayamkulam Kochunni has an item dance sensation Norah Fatehi, and you all know how it sounds. However songs that are simple in lyrics and good music attract outsiders. The best example is Jimmiki Kammal, ollulleru from Ajagajantharam, kudukku from LAD, etc became a sensation outside Kerala. Kaduva's Pala Palli Thiruppalli is a peppy banger and belongs to repetitive song or refrain song genre. A quick internet search gives you the special factor about this genre.
Why songs are so relevant? Because songs brought people to the theatres. Up until pre-Jio revolution, it was the most successful way of marketing a movie. Now we've digital posters, teasers, trailers, interviews, PR shows, reviews, trailer's teaser and what not. Heck! Even today, you cannot discard the potency of video songs for theatre occupation. Arabic kuthu (Beast), Ponni Nadhi (PS-1) are some recent examples.

1. Next is Action performances:

Until the 1990s, Malayalam movies completely ignored the value of action sequences and rarely had any concept of superhero or macho heroism. Meanwhile Tamil movies created this genre and perfected it with stars like Rajinikanth, Arjunkumar, Sarath. This genre still continues with actors like Ajith, Karthi, Dhanush etc. attracting many youngsters, particularly boys and men to cinemas to enjoy such superheroism and action sequences.
Rajni's 1995 film \"Muthu\" was dubbed in Japanese titled \"Muthu Odoru Maharaja\" gaining him a cult-like status in Japan. Although a remake of 'Thenmavin Kombath', the screenplay was largely re-written to bring in machismo by adding new plot details and characters.
We also tried copying the genre and had both ups and downs. Shaji Kailas and Joshiy came at the top mastering this genre but when their films started saturating with similar themes, couple of the subsequent ones bombed at the Box office. Mohanlal, Dileep tried a bit of Rajinikanth in 2000s, only to end up losing BO and finally came back to their common man image. And its again this deficiency which helped Tamil movies.
Youngsters wanted action hero movies which are still low in Malayalam, and Tamil movies filled that gap. Whereas such movies aren’t much patronized by Malayalee families. So there is no scope for making such movies in Malayalam. If at all if Malayalee audiences preferred these genres, it had to be rooted with Kerala culture. So you get Feudal stories like Aaram Thampuran, Devasuram which saw protagonists as larger than life. This helped both the sides of the weighing machine. Kerala culture and familiarity for the families and machoism for the youngsters.

1. Next is the MOST IMPORTANT REASON:

We had a dumb concept of classifying theatres into A, B, C classes where A Class theatres represented the traditional air-conditioned theatres in city centres which were called Releasing centres. The B and C class theatres were poor in facilities and hence were not given new releases at the time of the release. This concept existed because Class A theatre owners used to fund the production of the movies protecting their interest. So when a new Malayalam movie gets released it will be played only in A Class theatres for the first one or two months and then trickle down to the B and C.
An old news report briefly mentions the releasing disparity
Meanwhile, Tamil movies enjoyed wider release in Kerala irrespective of A or B or C class theatres. So, many B Class theatres played Tamil movies much longer until they get a new Malayalam release. So people in smaller towns, village areas patronized a lot of Tamil movies. This helped many to be familiar with such movies and enjoy it, which further fuelled more interest leading to the rise of Tamil movie stars fan clubs etc. It was only recently Malayalam industry broke this stupid ritual and embraced the wide releasing culture.

1. Language Barrier:

A good percentage of Tamil words are there in Malayalam vocabulary and are easy to understand, so they're mutually intelligible. However, there is an interesting aspect here, Malayalam has a lot of Sanskrit words and pronunciations even in causally spoken Malayalam. In addition, Malayalam has the highest number of loan words from other languages like Arabic, Japanese, Dutch, Chinese, Portuguese, Hebrew etc out of all the Indian languages. On contrary Tamil has least foreign languages influence in its local parlance. So did the influence of Sanskrit too. This makes Tamilians find it harder to understand Malayalam used in Malayalam movies, while Malayalees who have Tamil vocabulary in the Malayalam language find it easier to understand.
From Tamil, we jumped to Hindi, Telugu, Kannada, we crossed continents to watch movies. It became a socio-cultural zeitgeist for malayalee cinema-praanthanmaar. We weren't defensive about exposing ourselves to different languages and culture that is alien to us. There could be multiple reasons for it. My speculation says it's 'the diversity within our geography, the literacy rate, the limited media culture promoting Hindi through Dooradharshan channels and AIR. Speaking of this, I remember now a globally held filmmaker or someone highly regarded, mention a small place in India called Kerala has the most refined cinema audience. I'm unable to recall his/her name. Anyway....

1. Next is, Actors in the 80s and 90s:

Actors themselves were catalyst in fuelling our viewership of Tamil movies. A lot of the Malayalam actors have acted in Tamil cinema in both leading and side character roles. Mani Ratnam's celebrated movie "Thalapathi"(1991), showcased Malayalam actors like Mammootty, Shobhana, Manoj K Jayan etc. This caught the eyes of many malayalees to engage with Tamil cinema. Kamal Hassan, Chiyaan Vikram, Rahman, Seema, Urvasi, Bhanupriya, Geetha, Ambika etc. have exchanged good amount of screen time in both the industry promoting the lopsided viewership. This trick is still employed by current gen directors like Lokesh Kanakaraj for wider market and talent factors.
\"Thalapathi\" a 1991 Indian Tamil-language gangster drama film focused on a universal theme of \"Friendship\" with an ensemble performers from Malayalam industry

1. Production value:

The current generation and our successors will be oblivious to a fact that once upon a time cinema was nothing but magic. Before tech for making a film was affordable, before the learning of a skillset was abundant , before millions in our country could alleviate themselves from poverty, before the globalization and the internet etc.. The concept of CINEMA was nothing short of a magic. Nobody knew and cared how it worked. You sit, the lights go off and you brace yourself for magic. You see few humans projected on a white screen and believe they're out of the ordinary. The transition from a mute Black&White frames, to B&W sound and to a colour encoded frames were witnessed with a sense of amusement in increasing degree.
A beautiful article where the author recollects her days of watching a movie in a small town.
Well, this was how it was perceived by a large segment of audience in the initial inception of cinema but towards the 80s and 90s, the potency started wearing off because "familiarity bred contempt". In order to keep this suspension of disbelief that cinema once offered, Production houses started scaling up their projects with big budget.
This led to an extraordinary scale of production values that was unthinkable in Malayalam. Shankar's Jeans (1998) became a talk of the town because of the song that was shot in seven wonders of the world as well as the massive use of VFX that was unheard of that time.
Shankar's \"Jeans\" filmed in & around the Pyramids of Giza - Egypt.
I'm not sure how much the younglings of this sub can relate to it. We are over exposed to new cultures and worldly experiences through other people's eyes/content in social media, that it has worn out the novelty factor associated to it. But for our predecessors vallapolum ulla big budget cinema was the only source, for this experience. In order to familiarize this cultural gap, I recall this scene from Vettam where Mani's character is in awe over an Elevator that today's world take it for granted and is too mainstream. Something so silly but can provide valuable insights for an anthropologist.
Even today, many Tamil movies are patronized for watching something astonishing that we normally can’t see in Malayalam. Forget Tamil cinema, cinephiles everywhere adores commercial cinema with huge set pieces, explosions, destruction, exotic locations, VFX etc.

1. Media culture:

Sunnetwork, a mass media broadcasting company headquartered in Chennai, Tamil Nadu operated many prominent channels like Surya TV, Kiran TV which aired a lot of Tamil movies and songs pushing our affinity for Tamil movies. To a post 2000 malayalee generation, this media culture was a normalcy and so became Tamil movies.

1. Cultural exchange between Students.

Youth is the biggest consumer of cinema. How and why is a different topic on its own. Anyway, an exodus of students filled the surplus amount of institutes in Tamil Nadu, influencing their interest in Tamil cinema.
Combining all these relevant small and big factors, and them actors being at the right place, at the right time led to this humongous fandom. So, it was never completely about Malayalee audience ingratiating the star worship or it being a predicament of unemployment. Nevertheless, it must be a part of a bigger picture but never painted the whole canvas is my point.
Now let us try analysing few of the factors that put Vijay on a separate pedestal in Kerala's fan culture.
Firstly, Vijay's genetics. He may not be a Greek-God like figure but what he has is a next door boyish charm looks which is the actual selling point, alluding an impression that he's one of us. He has a "rags to riches" synonymous story (not exactly per se but in the initial stages he was dismissed on few differences) which helped even one of our PM for populism, even though the narrative is diluted.
Secondly, his over achieving skill sets. His graceful dancing skills hasn't faced a competition in so many decades, songs he has sung has been chartbusters, has great flexibility and athleticism for action performances etc.
Next is his Off screen persona and the most important factor here. Before I speak of this, I want you to understand a fact which brings a large audience for an in and out mass masala films (which is a personal umbrella term for me, for every commercial media across the world, from Hollywood's Superhero films to East Asia's Anime) and that is the "Main character syndrome." These mass films cater to this rudimentary feeling in each one of us. As we engage in such a film, the protagonist's real life identity cease to exist and we perceive ourselves on the screen going through all those challenges. Well, this is universal to every actors but in Vijay's case, this event is extended beyond his reel life.
He speaks very little in public spaces offering people to make their own assumptions of him (and when he does speak, it ends up as a sensational news). So he is what you think, which is again an extension of you. His humble and down to earth low public profile boosts his brand. Actors who realizes that mass superhero roles are a meagre gateway for a viewer's main character syndrome, will preserve their title for decades. This is why actors like Yash and Prabhas has maintained a low profile despite being at the helm for overexposure after their blockbusters. And the reason why social media stars are quickly forgotten. There's a name for this social adage that I can't recall at the moment.
And did I mention about production houses playing their active role in promoting their movies for larger audience in order to recoup their investment? They partner with leading distribution houses in Kerala and make huge promotions. So, even if an actor like Vijay refrained from growing his stardom, the big power houses would do it on his behalf owing to market sentiments.
Lastly, Vijay has decent acting chops and had a good career choices ranging from rom-com, action, drama, thriller. His 'Thulladha manavum thullum' and 'Kushi' still holds a special sentimental value among oldies and newbies. His teary eyed roles and humour timing hasn't been awkward as such. Otherwise malayalee audience wouldn't patronize an entertainment only packaged joker. It was post "Ghilli" that he stuck to a single dimensional superhero for cinebiz which after a decade of decent to good script is now showing signs of slowing down from repetitive theme.
23 years of Vijay and Jyothika's \"Kushi\"
So, these are the ones that I've observed and if you believe there's another major contributing factor, please pitch in. However, tribalist mentality among clubs and fans aren't the fundamental factor that established their presence in our pop culture but was merely a cherry on the top that cemented their position further deep because tribalist mentality is never about a person or an ideology but about one's own ego. The ego that my opinion can't be wrong.
In the coming years, if stars like DQ gain a total control over pan-Indian market, one mustn't hastily conclude it's all owed to his PR or his looks. It could be a contributing factor but the nuances leading to that status is far more oblivious to an average cinephile because it involves a lot of socio-political factors too. The same goes for an institution, a political party, a religion.....the nuances are huge and breaking it down to a single simple factor is a simpleton's way of thinking.
This post's information is catalogued from various discussions across the internet, from boomer cinema Facebook groups to RMM. I've tried to archive it at one place. Thank you.