Amex pays cashback here, other cards have done this before too. They don't pay that out of the processing fee here, that's paid out of the 27.3% APR you pay for

Amex pays cashback here, other cards have done this before too. They don't pay that out of the processing fee here, that's paid out of the 27.3% APR you pay for any outstanding balance at the end of the month. But you seem to think you're winning with retailers needing to put prices up to pay you cashback. Great system.