Interchange fees are capped, but the fees your payment processor charge you are not - it’s just that the payment processor makes more money now. (If you’re not

Interchange fees are capped, but the fees your payment processor charge you are not - it’s just that the payment processor makes more money now. (If you’re not a risky customer, you should be able to get that way down now.) However, Amex until recently qualified for an exemption from those caps, hence being able to provide a useful cashback scheme.