"I simply do not understand why companies of any size keep falling for this, when if I had only ONE shop, I'd have a backup card device under the counter."
I'm thinking that the till does more than the money. Perhaps stock control and logistics depend on knowing what has been sold that day? But then there could be emergency forms to print out and biros for staff to tick the boxes, so I imagine it is all down to how much you budget for a 1 day in a thousand occurrence.
Icon: the green grocer I got sent to as a boy had a wooden till with a brass handle. The shopkeeper added up the costs with a pencil on a corner of a brown paper bag. The veggies came from a market garden a few miles away.