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.