As proved by various outages, when electricity (or the internet, or the service provider, etc) is down and prevents digital transfers being made... cash doesnt work either, cause it's all the same POS / accounting software that handles cash which is also down.

Also if a natural disaster takes out internet access for an extended period, wheres the cash a business needs to keep on hand going to suddenly appear from? I haven't worked in retail in a decade or more, but we always kept as little cash as possible on hand due to the constant threat of robbery. Even back then cash was way less than 50% of transactions, I'd be surprised if it was even in the double digit percentages anymore.

Cash does have a cost

It's a pain in the butthole tbh.

From a checkout chump perspective it was probably 40 minutes of my day wasted dealing with the cash. Getting it dispensed, double counting it all, depositing in to the safe when you had too much, watching out for dodgy currency or those dickheads who try the quick "I give you a 5 and you round up the change to 10 and then I'll swap that for a 20 and then give you 30 so I get a 50" scam, dealing with damaged or defaced currency, recounting at end of day, getting reamed for being too far up or too far down in the count, having to sign forms to swear to god you hadn't knocked off a pineapple (or put too many pineapples in the drawer)...

Then you need a safe storage space for the cash, security to protect the cash, literally a whole industry built on transporting it around the place, keep enough cash on hand to provide change, keep enough to cover EFT withdrawals.

There's a lot of cost to handling cash. Also its gross. Did I mention its gross yet? Getting warm notes that were slightly sticky was disgusting.