This is it entirely.
Any time you bring money and sexual gratification together, the depravity in the content will escalate rapidly. Anyone who wants a piece of the market has to do something different to stand out from the crowd, and that often means more extreme and nasty shit. Standard vanilla cheesecake is a cornered market, so newcomers (newcoomers?) have to go for more shocking stuff (or more niche fetishes). It's incredibly hard to verify that every person in porn is of legal age and consenting enthusiastically, and it gets harder still to verify once you start bringing in violent gonzo shit.
I think the people who run payment processors know that money is the factor that leads to the degeneracy. And they don't want to be the direct cause of CP, bestiality, snuff, etc. But no platform can afford to manually vet every single content creator, so they have to shut it all down.
'Artistic nudes' (of adults) are usually still permitted when this happens. Nobody ACTUALLY cares if you sell tiddy pics, they care that men go out of their way to pay for illegal shit if you give them even the slightest convenience.