Yiff.party is actually voting to remove creators that are not creating porn, BUT are only removing creators who make porn of real life people. Think deepfakes of celebrity's.
Patreon has no where to read on what their doing, but they have been cracking down once and a while on people who make 3D Beastiality or SS/Loli content.
Sum has had problems with them in the past over his content, but now their gripe this time is that content he has made is now on sites where people can view free of charge (F95, Multiple Boorus), instead of being behind the Patreon paywall. Which is dumb, because its more of a their problem that they expect creators to fix. And then again, there's always most likely a patron that will take said content and post it wherever anyways.
So in short, Patreon is trying to fight Piracy (See The Gaming Industry) and types of Porn. Or Sum is just shifting to make his stuff less obtainable, which you can't really be mad at and at the same time anyone can always become a Patron, download, and share, like its always been done, it'll just be more of a process on both sides.
If Sum does lose his Patreon, Subscribe Star is an option, but they eventually will get the same sentiment Patreon has. The only other ways are through donations, possibly KoFi, and there's Pixiv with its premium page for artists.