There is nothing stopping stores from offering a discount if you pay in cash or debit. Businesses most often choose not to, so they must feel like they are getting somthing out of the deal.
It's probably different when you're at a much larger scale than I am, but even Wal-Mart (who I was employed by in my late teens) has all sorts of cash-handling procedures to mitigate the risk of money just walking away. Even a their scale, they spend 1% on CC processing, but by the time they added up all of the labor and expenses of cash handling,it might be comparable. And for a small business it's likely more.
And then there's the data collection which has value too.
People act like accepting cash is free, it is not.
Realistically, the price difference is probably not worth the hassle of needing two prices and card sales are probably affordable enough and common enough to not bother.
https://www.ca5.uscourts.gov/opinions/pub/15/15-50168-CV0.pd...
They basically said a surcharge for credit is effectively the same thing as a discount for cash, and because of freedom of speech, merchants are free to communicate the difference to their customers either way.