If these places can get 10% more business because people aren't fumbling with cash and the process is sped up and the same every time, the fees will be offset with the added business. There are many times I've wanted something, but not bad enough to stand in a long line and then I just skip it. I'm sure I'm not the only one. Cash is not fee-less for a business either as there are deposit fees at the bank. Everything has a fee nowadays, so may as well make the process as fast and easy as possible.
Not saying this has happened, but one other thing to note is maybe they've had issue with cash not adding up....a few too many buckaroos hitting the tip jar instead of the till, or just math incompetence. If you've ever worked anywhere with a till, you'll know that there's always someone whose till never adds up at the end of the night, even if there's nothing nefarious and it's honest mistakes along the way. Easy to make mistakes when in a hurry and the line is 25 deep between quarters or periods.