PR risk. US evangelicals exert a lot of pressure to apply their particular censorship standards worldwide. The literal puritans.

It's not 1999 anymore.

The only thing the payment processors really have to fear at this point is the government itself asking for a bigger pound of flesh than they already take or sticking its fingers in their business to increase its own power (perhaps at the behest of other interests) like the did with Backpage. The avenues by which the government would manufacture the political will for such action would likely be the tried and true "but the children", "terrorists", "trafficking" and the like, perhaps with a modern BS twist on it.

The "christian right" boogeyman basically doesn't a) exist in the volume that people like you pretend it does anymore b) care about adult content anymore seeing as the overwhelming majority of people in the western world don't really remember a time before internet adult content and just take it as a fact of life, this stuff just doesn't really move the needle for anybody anymore.