This is misrepresenting the point of sites like Patreon or Subscribestar. The point is to support the creator while they work on their products. Almost none of them are able to up and quit their day jobs. They have to spend tons of extra hours alone, avoiding family or friends, trying to develop their games. Buying a finished product is great, but a creator's potential success is limited by several factors, including whether they can still eat, pay rent, etc. Supporting creators doesn't only help them buy better hardware for improving the quality of their equipment and the turnaround time for releases. It also moves them closer to being able to work on their software full-time.
I get wanting to buy a finished product, and I am happy that you buy on Steam or elsewhere that sells completed games. And, of course, you're free to choose not to support someone on a membership platform like Patreon. But there is also a real need for support in the mean time. Consider, for example, novelists who get an advance on their books' sales; or small start-up businesses that get loans from banks or venture capitalists to invest in their businesses. This is the same idea with sites like Patreon and Subscribestar. Unfortunately, the current model is flawed, because obviously some creators abuse the system.