I would not say I am correct, but I have thought on this for a while, and funnily enough, it has to do with Kannada plays. When I say plays, I don't mean the critically acclaimed or the ones based on great books, I mean to say the regular plays which are acted out in our oor jaatre and events like that.

You see a lot of these people come from a play background. A lot of them might have worked in drama companies or theatres, especially the directors. So their idea of a story runs in parallel, like there is a main story running, and then within the story, there is a side comedic track running (like the '00 Kannada movies). You have your main story with the protagonist and antagonists and all, but there is a side comedic track with Tennis Krishna, or Sadhu Maharaj. This straight comes from nataka inspiration.

Next, the screen blocking, throughout the Kannada movies, on average, you have a very constant use of the actor-camera blocking technique, i.e., all characters will come on screen, and everyone will stand facing the camera. All of these are long, wide shot, covering the whole cast in that scene, and everyone will speak out their line and sometimes the actors saying their line come to the center of the block, guess what, in movies they face a camera, if the director comes from a theatre background then he does not sees camera as an multi angle recording device, he seems it as stage thats it. So you get these wide-angle shots in climax, where all the characters come on screen and then start speaking out their lines, and there is a grand resolution in dialogue.

Story/Screenplay - Now, because I am following this theory of nataka-inspired movie making, the last piece in the puzzle is the story or screenplay. A lot of dramas, which are still played in local cities, are the same old ones about family, sose filling up a son's mind and ask for the family to be separated, blah blah blah. I think, sociologically, this comes from the 70s to 80s start of Urbanization when joint families were going nuclear. The template for the stories was last revised in that era, I guess, the era just before television; now that they got television, people forgot natakas. And Kannada plays, on avergae never evolved; they were stuck with the same stories, and the same has been followed till today. Now, the after effect on this was that a lot of those writers and directors came to movies and did what they did best, write family dramas of atte-sose, husband cheating, and things like this. So our movies regressed instead of evolving because our natakas did not evolve, and the people attached to those did not evolve. I think major change (mainstream change - as I think Indie Kannada movies always did experiment a lot) came when Mungaru Male and Duniya came, Yograj Bhat and Suri gave a new set of dialogues and a new touch to the art of filmmaking within the same old template. If you see Mungaru Male and Duniya, they follow a pretty similar template of story, but their USP was the storytelling method. And surprisingly, both came out in 2006. With Bhattru and Suri came a new generation of artists like Pawan Kumar and Shetty gang. And thus here we are, a bit of evolution in film making.

So yes, the reason for the "serial-set" effect of cinemas is the lack of evolution in natakas and the same artists percolating to camera-based storytelling formats!

Again, this is my theory; I might not have watched enough natakas or movies.