Earlier quoted context omitted.
Why should payment processors force them to. They will make less money
Probably the reputational risk to them from being associated with porn is not worth whatever OnlyFans brings in.
For decades, the specific issue was with the huge chargeback/fraud rates associated with online porn.
- People paying for porn with stolen cards
- Or, more frequently, people disputing the charges when their wives see the credit card statements and get mad, so they claim the card was stolen etc.