Valve confirms credit card companies pressured it to delist certain adult games

What can be done to loosen card companies' grip on this? It has been a constant problem now for decades.

Likely nothing.

The simple fact is, Visa/MC don't want to deal with porn because the number of chargebacks and fraud from porn purchases is significant and a huge outlier compared to most other charges. Their crusade against processing charges for adult material isn't about purity, it's simply business.

I doubt it. If that were the case, I think they would only be complaining to Valve about the number of chargebacks issued from the Steam store. Not about genres-that-are-correlated-with-chargebacks-in-other-contexts.

Given Valve's generous refund policies, and the fact that a steam store purchase on your credit card statement looks quite innocent, and that the credit card companies didn't complain to Valve about chargebacks but about content, my guess is there are hardly any chargebacks, and this is just about moral purity.