>For specifically sexually explicit stuff, it's because chargebacks are __significantly__ higher for these types of purchases.
This has always been a lie. I work preventing stolen credit cards from being used to buy gift cards.
Payment networks do not at all care about cutting you off for having chargeback heavy flow. They demonstrate their value to customers by supporting those chargebacks, they make $20 for every single one. If you have a large fraction of your payments causing chargebacks, they just charge you more money for the privilege. They won't cut you off unless you are obviously not doing anything to prevent credit card fraud or are party to the actual fraud itself. Payment networks don't even do that much to prevent fraud, because it doesn't hurt their business at all. Everyone knows you are protected when you use a credit card, and frequent demonstrations help that.
This has always come down to some fundamentalist "Christian" groups who keep spending big bucks suing anyone they can find who sells anything adult, and suing Visa and Mastercard as accessories. They are trying to ban porn, toys, adult content in general.
https://en.wikipedia.org/wiki/National_Center_on_Sexual_Expl...
This is the group that drove Pornhub to delete 9/10ths of their library.
Compare their efforts to the australian group who got so much flak for demanding steam remove violently rapey games and yet are fine with steam still being full of sexually explicit games that aren't about simulating abuse.
I can't understand why people believe this lie. If it were true, you would not be able to buy a gift card over the internet at all.