I think the problem is that merchants hate the card networks and consumers generally like them and there are a lot more consumers than merchants. If you are a politician, which block of voters are you going to side with?
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).
Merchants don't hate the card networks. That's a minority in my experience, who are penny wise and pound foolish.