Good reason to accept cash is that you have a chokepoint on card transactions, the processor that handles the transaction from the store, and routes it to the bank. They outsource all the IT, and it is only a single keystroke mistake away from having a RBS month, where customers were completely unable to use cards, people were losing houses to foreclosure because debits did not go off, and people could not buy food, electricity or gas, plus were not being paid, as the money went from the sender account, but vanished into nothing. All because somebody in a outsourced data centre, with only a sheet of instructions to follow, not even at any way computer literate, or fluent in English, mixed up 2 steps in the process of completing a day transaction batch, and overwrote the entire database by attempting to restore from an empty backup. Took a good few months to get them more or less running again, and cost them a good chunk of the customer base as well.
Choke point, in that all banks use the same 2 processors, Visa and Mastercard, represented by me by SASWITCH, and a failure at one will cascade through to the other rapidly, leaving no cards working, and even affecting ATM operations, as they also use the same switching networks to allow other bank use, and this comes before the own bank mainframe (or emulation) is able to process the transactions, and a lot of the internal bank systems are also linked this way. Very common to have 10-20 minute outages on the networks at times, but not noticed by customers much, as you are not using them 24/7, but only for a minute at a time. You just see it as a error, and the store tries again, perhaps after a minute, and you are at the edge of the window.
By me 45% of the population is on welfare, with 7% as active taxpayers. So 45% use a card, and have little issue with it to get grant payments, and the vast majority are older women, and single parent households bringing up children, plus a lot of child headed households. Card gets used once a month to draw cash and buy food, and the banking system had been forced to totally block any direct debit ability from those cards, aside from a few select providers who have that in limited form, because of loan sharks that entered direct debits against multiple cards, and emptied them on grant day.