Many more restaurants and grocery stores don’t, and then it’s 2-5% of cashback vs. 0% cash discount. Doesn’t sound like a rounding error to me.

There are a lot of good reasons to dislike the market structure and game theory of card payments in the US, but please don’t accuse consumers of being short-sighted or irrational.

The only way to break the cycle of self-reinforcing incentives would be swift regulatory action. Absent that, playing the game is the rational move at the individual level for both merchants and consumers.