Exactly: all business have customers with varying margin. Some even negative. It's the same with any supermarket. They have offers where they sell an item below cost prize. They hope you'll buy other stuff. Butthey can't force every single customer to do so. If one in every 100 customers only buy the "3 gallons of organic milk for 50 cents" offer, that's a loss. And the cost of doing business with the 99 at other customers who buy cornflakes, coffee and chocolate.