> No idea why this is a thing actually

a) It still affects their bottom-line: the issuer might still try to dispute this using a different code despite payment scheme (formal term for Visa et al.) rules, and the merchant targeted is prone for fraud (for example, airlines have been hit with this by exploiting tourists looking for cheaper tickets by offering them suspiciously cheap tickets on seemingly-trustworthy websites by fraudsters and funding them by insecure cards)

b) Misinterpretation of mandatory rules: PDS2 is applicable only for EEA customer - EEA merchant, but some extended it for whole world despite the rules literally dictating the limits

c) Soft friction for encouraging domestic card usage: because of accept-all rules by payment schemes (and no local rules that allowed merchants in a region to reject international payments), this is a way to block US cards by guise of fraud prevention (because international cards are expensive for merchants to process)