How on earth does Tesco make a profit when it redeems Morrison's gift vouchers in store for products?

Whilst you are in Tesco using your Morrison's vouchers, there is a big chance that you will have a wee wander around the store and spot something that you like. It's a bit of a fly way to get you in there. Most stores use this same method now to entice customers in. I think it's pretty smart!!!