They are usually called loss leaders and they set a limit on how many you buy. The idea is to drive traffic by reducing prices on common items. Stores would s

They are usually called loss leaders and they set a limit on how many you buy. The idea is to drive traffic by reducing prices on common items. Stores would stock them because other stores would and all of the customers want them. Some stores would put a hot topping and sell drinks. Others would advertise other sales driving traffic to other areas of the store.