From Robert Towne (ultimately, Chinatown is an allegory about the film industry):

Jake Gittes: How much are you worth?

Noah Cross: I have no idea. How much do you want?

Jake Gittes: I just wanna know what you're worth. More than 10 million?

Noah Cross: Oh my, yes!

Jake Gittes: Why are you doing it? How much better can you eat? What could you buy that you can't already afford?

Noah Cross: The future, Mr. Gittes! The future.

That's what the producers want. Most of them have enough available cash to do quite nicely. It's about the future. And the control over the future.