This seems incredibly odd given that OnlyFan's primary payment processor is CCBill, a massive payment processor focused solely on adult content. Here is opportunity #3928 for Stripe to step in and earn their valuation and flex their payment muscle and allow adult payments.
It's very likely the pressure is coming from Visa and MasterCard (especially MC) rather than at the level of CCbill.
CCbill itself couldn't exist if Visa and MasterCard didn't let it process payments for porn.