Well, I could agree with you, but you're missing a point when comparing with other developers. This guy didn't do this when things were already going well and he was rolling in money.
The guy didn't even mention steam once when he was on patreon, right? Because things were going well there. Obviously, when he was banned on patreon and switched to subscribestar, everything fell far short of his expectations. I remember him saying that he lost 75% of his supporters. If he did this steam thing arbitrarily when he was on patreon, I would agree with you and have called him a milker asshole, but things forced him to do it.
Imagine a shop with thousands of customers in a great location and then suddenly the shop is forced to close and the owner has to set up the shop in a more remote corner and more than half of the customers no longer come there.
And after some time, when you get another good opportunity again, do you take it or do you say, "oh no, that's enough for me"?