You do realize PayPal was just as involved in this as the rest right?
PayPal didn't send Valve any written content demands either, its acquiring bank did the enforcing just like MC, but PayPal was a named target of the campaign, got its Steam payment rail severed over the content issue, and ended up in the FTC's crosshairs alongside the card networks.
Also, PayPal's aggressive posture toward adult-adjacent businesses predates this.
The Erotic Review piece described PayPal freezing a subscription business for six months with "no appeal process, no recourse." So PayPal cracking down on Steam over adult content wasn't out of character; it was the largest-scale demonstration yet of a practice smaller publishers had already been living with.