The card companies charge merchants for transactions. The merchants raise their prices to cover those transaction costs: For a very long time (and still, in a few places) it was against the card company's terms of service to have a card usage surcharge. A very few places now have 'cash discounts' or don't accept cards at all, but these are by far the exception. As a result, /everyone/ ends up paying for credit card rewards, even those who don't use credit cards.
The card companies charge merchants for transactions. The merchants raise their prices to cover those transaction costs: For a very long time (and still, in a few places) it was against the card company's terms of service to have a card usage surcharge. A very few places now have 'cash discounts' or don't accept cards at all, but these are by far the exception. As a result, /everyone/ ends up paying for credit card rewards, even those who don't use credit cards.