They're making the money either way.
It's called a loss leader, get you to spend $100 on goods with a 50% profit margin, then give you a portion back as a discount. How may times do you go into the supermarket to buy a few things, and then get conned into doing a major shop to get the discount is what they're thinking.
Either way, the small independents can't win, they close up, and the market gets more concentrated.
been there, done that!