The comments here seem to suggest that the loyalty program funded with credit card margins are to blame for the difference.

It suggests we'd be better of eliminating the absurdly high hidden taxes paid to the credit card companies, that in turn act to gamify the business. In the end they raise the cost of doing business, for virtually no benefit at all. It's a monopoly extracting as much wealth they can get away with.

The question at the heart of this: How can "the shining light on a hill" be so stupid? It's digging its own demise.