I'm so mad I can't pay with my card to play that DLC and the fact that Itch.io keeps the card option when it's not available is nasty. I really wish I could pay that DLC... :(
MasterCard and Visa are the major card companies that are pushing these restrictions. I'm sure there might be other card options out there as well, which is why Itch keeps it available. It wouldn't be fair to remove them all because of MasterCard and Visa.