I may be wrong but from what I heard there was a new legislation that was released in the US that has made depictions of underage boys/girls taking part in sexually explicit behavior illegal EVEN if it is an artistic drawing - including drawing, paintings, or 3D models. I believe the legislation itself has been in effect for a while but has been put down as unconstitutional by courts in the past, but the atmosphere may be changing and you can get in serious trouble these days. If you want to take a look at the law :
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. [18 U.S. Code 1466A]. So I cant really blame Patreon since one of the main offense is to be a distributor of these materials. So even if game devs migrate to other services as long the service is based in the US then they will face the same restrictions.