Because studio executives – just like the executive of most other companies out there – have realized that they don't need to actually innovate or risk putting money into uncertain new projects, when they can just take something that's already been done, try to pretty it up a little, and then sell it to people who'll go see it based on name recognition.
Why take a risk with new IP, when the old IP that sort of worked is already there? Just give it a new coat of paint and sell more of it instead, fire some workers (I'm sorry, "rightsize" the company), buy another yacht. Problem solved.