Some people (a vanishingly small minority, admittedly) will only use cash. But some more realistic reasons for accepting cash:
- 3% credit card fees aren't nothing when your entire business operates on 4-5% margins
- It's much harder to launder money if you're 100% cashless - if you have even a small proportion of legitimate cash buyers you can now funnel more illicit money through that
FWIW handling cash isn't free either. It can be 2-3% as well (depending on a lot of things like volume, change requirements and typical patterns, insurance can be less if you have no cash on premises, ...)
In many cases the cost of credit cards and cash are surprisingly similar. Especially in Europe with capped fees.
Not that vanishingly small once you start working with the poor. A lot of those folks don't even have checking accounts, never mind a credit (not debit) card.
This has been a real issue in a few places that have now banned cashless, because it puts a heavy burden on the un/under banked.
