Comedy, Drama, War, Action/Adventure, Horror/Suspense, Animation, and Martial Arts.
I think that covers them all, if your talking about these basic genres. There are sub genres too, like 'slapstick comedy'.
Hollywood is a business, and like any other business it is their job to make money.
Movies are extremely expensive! Halloween didn't have any real special effects to speak of, not even a drop of blood, and it costed them 100,000 to make. Back in 1978 or 9!And that is considered cheap!
What they like to do is take a block buster hit, and figure out what made it so appealing,then take that, and put it in other movies. Like if it was the story that was so great, like Jaws, they could just keep making more of that same type of story.
Anything and everything can be imitated from movies. I remember one director said something like, ' everyone steals from everyone else, no one is totally original', speaking of movie making.
So you will see common movies made every year, untill they fade. Its just like fashion
tey come and they go, but they're always replaced, with some new, fresh style.
Music is the exact same way.
As long as movies are being made, those basic genres will always be there.