They like the card networks because they are lured by point schemes, effectively money charged to the merchants and then shared back to cardholders. Consumers would flip in a heartbeat if shops were allowed to offer discounts to those not using credit cards.

I used to by all my PC parts from a shop that had a 5% discount for cash purchases. It was the sort of shop that was just a counter with all the merch hidden in the back. I don't know how they kept the CC companies from knowing but maybe 40% of their business was cash purchases (circa 2019).