Unless a retailer doesn't accept any cash, the marginal cost of accepting another cash transaction is low.
Consider a front desk at a hotel. Thousands of dollars a day in transactions occur via card, which would warrant frequent drops into an expensive safe if they happened with cash. With cards they pretty much only hold a trivial amount to deal with sundries that isn't worth protecting beyond a simple envelope to a back-office.
Credit cards dominate many industries in the US to a point where cash management is now trivial because the daily amounts aren't worth any employee losing their job over or a criminal risking robbery punishment for.
A business that has any type of daily cash accounting is still going to need to balance the register at the end of the day, reestablish change to open with, have arrangements for transport, &c. Bad employees can still pocket a tenner on occasion.
Sure, some smaller places with barely any cash probably just lock the drawer and call it a night.
I can't find the figures now, but estimates of cost of cash handling is far far lower than the 2-3% of swipe fees.
Many hotels have neither of these.
To the original point, if I am staying in the hotel and I go to the bar I would just sign to the room and not pay cash.