alt Hacker NewsI see random offhand unsubstantiated online comments here and there including here on HN, that 1) chargeback rates of porn, games, and digital contents are significantly lower than anything else, and 2) credit card companies already charge higher fees for porn despite that.
Combined with prevalence of the suspiciously well standardized "because porn users and gamers chargeback Steam purchases way too often" canned responses, I think it's just an excuse, if not "the" excuse somewhere - like the basis for using incorrect data for internal risk modeling or something like that.
I've seen the chargeback rates, they are low. Consider that most adult consumers are repeat purchasers (subscribing to their favorite artist/dev/performer). They do not want to get banned for a chargeback and lose out on content! Most adult content creators also have friendly voluntary refund policy when requested. So chargeback rates are very low in adult.
Meanwhile other industries like travel have crazy high chargeback rates. This is because it is notorious for a no refund policy / locking customers into purchases months in advance... and then people just chargeback instead of accepting a consumer hostile no refund policy. So travel ends up having high chargebacks... and yet has minimal trouble getting processing.