If scalpers (who have overheads of their own) are making money then that implies the restaurant is doing the economic equivalent of leaving a lot of $100 bills on the floor. Before those bills were being picked up by random customers but now they are being picked up by people who heard there were restaurants leaving $100 bills on the floor. But the cause is ultimately the restaurant choosing to just give up free money by not charging a price so that supply and demand equal and the market clears.