Rather than risk this liability it's easier for payment processors to just not work with high risk sites.
The first link is directly to NCOSE (Morality in Media) but heres a few other articles with quite a bit more information. [1][2][3][4][5][6][7]
[0] https://ncose.salsalabs.org/thankyou_mastercard_visa/index.h...
[1] https://www.newsweek.com/why-visa-mastercard-being-blamed-on...
[2] https://knock-la.com/onlyfans-bans-sex-work/
[3] https://reason.com/2021/08/20/why-onlyfans-is-double-crossin...
[4] https://www.bbc.com/news/world-52543508
[5] https://www.thedailybeast.com/the-real-reasons-why-onlyfans-...
[6] https://avn.com/business/articles/legal/mastercard-visa-ban-...
[7] https://www.reuters.com/article/us-pornhub-policy/pornhub-pu...