Wise cards are issued in your country of residence. It's very tricky to get US card remotely as UK resident. Only way somewhat accessible to normal people is AMEX global transfer, but even then you need to have ITIN and US bank account.

AFAIK you cant just assign non-US bank card to a billing on US Apple account. At least it was the case before and at least for purpose of switching account region.

Thus you use USD gift cards since they easy to buy.