4chan

You're not wrong… but as you said, those are external costs. While it's fine to wish for a simpler, more equitable system, given that the prices are mostly the same no matter how you pay, wouldn't you rather be part of the group receiving the benefits? Paying with cash or check or a non-reward card is leaving money on the table. The cost of handling cash and checks isn't necessarily any lower than credit card processing fees and people don't have much tolerance for strange new forms of payment, which leaves merchants without much leverage to push back against rules which prevent them from passing on the higher costs of the reward cards to those using them.