I know. But I also know that if NSFW content makes up the majority of your store and/or sales, it behooves you to find a payment processor who accepts that risk (albeit at a higher cost).
Funnily enough, I bought lots of stuff on GumRoad and wasn’t aware that NSFW is huge there. I only knew it as the platform for online courses, ebooks and mediocre notion templates
Then the artist can take on the risk by establishing their own business and finding a payment processor who accepts that risk instead. Will they? Won't they?
If everyone on your platform does that, you no longer have a platform though.
Banning/outlawing the majority of your users, no matter how annoying or costly they are, is generally not a winning move for a platform that lives off its users.