And well you should, because that freebie-ness and the resulting multi-billion dollar transaction fee golden goose are the result of the merchant agreements that the card companies (MC, Visa, AmEx, Discover) make merchants sign. Since the 2010 Dodd-Frank Wall Street Reform and Consumer Protection Act, merchants are allowed to offer customers discounts for paying cash, or charge a service fee for taking credit and debit cards. (My county charges a 2% service fee for putting my property taxes on a charge card.) The CC companies' merchant agreements say that merchants can't advertise two different prices, but some gas stations seem to do it anyway with impunity. (No one cares?) Anyway, the bottom line is that most consumers want to pay with credit cards, the CC companies know that, so the no-advertising cash prices rule manipulates the system to some degree. I occasionally ask for a cash price on big ticket items, but since every card I have offers me a baseline 1% cash back, it takes a pretty expensive item to get me to save a net 1% (most transaction fees are about 2% for large purchases).
All of these shenanigans makes gaming the system practically a patriotic duty.
It's also profitable to game the other side of the transaction, and own MC and Visa stock, which are the pure plays in this market.