You are getting this wrong. It isn't his project that is the cash cow. He doesn't need to stick with a project if he gets bored of it. He can move on, create another and people will pay.
It is a fact that his income multiplied due to Milfy City but he, as well as anyone else, could see for himself that people remained and kept paying HIM when he wasn't releasing anything. For years.
People aren't paying him for Milfy City. People started paying him BECAUSE Milfy City. But they pay him because they believe in HIM. It is key to understand the difference here. Milfy City was just a bait and not the cash cow. It is his patrons whom are the cash cow. Milfy City was just a green pasture to attract the cows. As long as he can maintain the illusion of such green pastures, the cows will stay and he can continue milking them.
He isn't killing the cow. In fact, he is trying hard to keep the cow. Well.. hard.. he isn't very good at it to be honest buuut this cow is a very easy one to please for whatever reasons