That's not how the payment market works, though. If a customer walks into your store and has exactly one (type of) card on them that they want to use to pay, y

That's not how the payment market works, though. If a customer walks into your store and has exactly one (type of) card on them that they want to use to pay, you have a choice of accepting that card or losing their business. This makes competition between payment methods at the POS structurally very hard.