I'm not sure I buy the chargeback angle. It's commonly trotted out as a reason card companies would enforce censorship, but it doesn't make sense with the actions they take. Chargeback fees are paid by the merchant regardless of the chargeback's success, and are supposed to cover the costs of administering it (and then some). The very selective rules applied here are pretty odd from that angle too, if adult content chargebacks/fraud is the issue, then all of it should be the issue, not small niches.

Fraud is likely more realistic of an issue, but that's probably an issue with games in general, not just adult titles.

There are already high-risk merchant accounts with higher fees and cash reserve requirements, but AFAIK companies like Valve aren't being given any options other than comply or be destroyed.