Cash is king, especially for small businesses. You may have noticed more businesses requiring a mimimum purchase amount before they accept a card. Every time you use your credit or debit card businesses lose 1%-3% of your bill.
That cashback that Discover Card advertises? That comes from a charge to the businesses. That is why you don’t see Discover accepted everywhere.
If you want your favorite business to keep serving you, pay in cash when you can, they will appreciate it as profit margins are getting tighter and tighter for them.