We live in a society of disposable things, everything is disposable after being used for a short bit and entertainment is like that too.
I come from a poor farmer family that lived in a time where things were made to last, you bought a fridge it would last longer than your life, same with a toaster or a TV or whatever else you would buy. Now we buy something we are lucky if it has a 5 years warranty, a toaster might last one year if it is used once every day, stuff like phones get "obsolete" in one year, games and movies are mostly for entertainment at the moment, they are shiny and distracting for a bit then lose their charm fast, and why is that?
The answer is money, we live in an age where the average consumer has more money than they need or have their priorities all messed up, people have so much money they don't mind spending a lot for a new phone every couple of years, or buy so many games they will never finish or even play them at all, people pay money to go to the movies and have fun watching the new shiny *insert whatever movie franchise you want here* and then move on after a bit.
I am glad people have money and most will never know poverty, that is a good thing for sure, but it is also true that one only know the value of what they have once they lose it and that is the thing, the average person don't value their money, specially when they don't even earn that money and it's their parents that buy them the games and stuff.
Also thanks to the new technology humanity is actually losing their attention span, there are recent studies that say the average human today has a shorter attention span than some animals, because thanks to the new technologies we can just jump from one thing to another, we can watch a video and then read an article and then jump into a game in minutes, if we get bored doing something we just change into doing another almost immediately, which also contributes to the entertainment being made just for the moment, most gamers today would get bored of long dialogue based RPGs for example because they have short attention span and reading in a game is boring because it stops the action.
So those are the two reasons I think the entertainment industry is always playing safe and do the same thing over and over without taking risks: People have too much money and so they don't mind spending it in something fun for a short bit and they get bored of things fast so if entertainment is not "disposable" it would make them bored.