Because big business is about low risk, high reward.
Remember how the Silent Hill movies went? They made one very good movie, but their executive meddling changed it to be as appealing to as many people as possible with arbitrary shit like "people will relate more to a mother trying to save her daughter than a father trying to save his daughter, make the protag a woman".
Then for the sequel they spent the minimum amount of money possible, virtually all the effects were just for the trailer. When you remove the trailer scenes its just a rehash of one of the teenage girl "you are the special chosen one who has a cute boy sidekick" movies like Twilight and Hunger Games. Also, it was marketed as being a 3D movie in a big way.
They spent almost nothing, and made huge bank by killing the franchise intentionally coasting off the goodwill from the first movie.
That right there tells you exactly why mainstream media is trapped in a cycle of shit. Because you only make something good in order to have to spend less while still getting people coming back. You only invest when people stop showing up.
Batman #1 has to be flashy and show promise. By #12, it gets pretty shit so they have a Jim Lee alternate cover. Then by issue #16, you have a massive THEDCUNIVERSEWILLNEVERBETHESAME event book that sells all of the main titles. Finally by issue #24, they just reboot back to another shiny and new #1 that promises an interesting story arc it will never deliver.