I knew, sort of tangentially, a guy who wrote scripts for a living. He would write a script, then sell it to a studio. Usually it would just sit on the proverbial shelf and never get made into a movie.But a couple times they actually optioned something he wrote. What followed was a rewrite process involving no less than six other authors that were tasked with adding things the studio wanted into his script. No love story? Well, we'll just have to shoe-horn that in, because otherwise the women might not see it. Anything offensive to a major market, particularly China? That gets ripped out. Does it have merchandising? If not, we'll add characters, or robots, or whatever so we can sell toys and video games.
Etc, etc. The script that actually gets made bears no resemblance to his original work, and more importantly, they turned his original scripts into Generic Hollywood Movies that were virtually indistinguishable from the others.
The real problem here is for a couple decades nearly every well financed movie made money. So the studios analyzed just what a successful movie needs to have and created an assembly line to produce them. After awhile audiences were bound to look elsewhere for something new.