Even if they were popular enough to fill the seats they still lose, as they still lose those employees spending time on the phone to take the initial arbitrage reservation & then they lose time on the phone once again when the employee takes the arbitrage reservation cancellation call.

Yes, and they would lose this time with the man who books 3 restaurants because he doesn't know which one his girlfriend wants to dine at for their anniversary, 10 fake reservations from a competitor trying to block out a weekend night, etc.

Managing reservations and paying employees to man phones is part of the operating cost of a restaurant. Not to mention, this could be automated with software that ties customers to credit cards and reservations.