Well if you can get $100 worth of X on credit card for $98, but you can buy the same thing with cash for $97, aren't you actually paying 150% of the "cash back" with your own money? ¯\\_(ಠ_ಠ)_/¯
Merchants rarely offer cash discounts in the US.
Even if the merchant pays the sticker price for card acceptance, it's usually just below 3%, unless international cards are involved. Add to that the fact that cash transactions in restaurants are often accounted for in "more tax efficient ways", and it feels even more icky.