People who pay in cash are subsidizing the store’s costs to handle cash. Paying employees to count the cash (usually after closing), putting it in the safe, distributing the cash to cash registers, refilling when they run out of change, paying for the security service (Brinks etc) to deliver cash to/from the bank, insurance against robbery...
Cash is not free for a store to handle. Stores pay transaction fees on credit cards, sure, but they save on all the costs of cash. A hypothetical store that takes credit cards only would not have any of these costs and their vulnerability to robbery/theft would be limited to merchandise and capital only, saving the cost of insurance against theft of cash. For some types of businesses (services rather than retailers), this makes their office a pretty unattractive target for burglars and eliminates employee theft of cash.
Cash is not free for a store to handle. Stores pay transaction fees on credit cards, sure, but they save on all the costs of cash. A hypothetical store that takes credit cards only would not have any of these costs and their vulnerability to robbery/theft would be limited to merchandise and capital only, saving the cost of insurance against theft of cash. For some types of businesses (services rather than retailers), this makes their office a pretty unattractive target for burglars and eliminates employee theft of cash.