The entity liable wants to know that the coupon was the thing that pushed you over the edge to buy the product. People who would have bought it anyways generally don’t bother with the coupon.

I never knew the part about an entity separate from the seller being responsible for the coupons, interesting. But the second sentence I quoted is what I'm responding to. Coupons in brick-and-mortar stores may work like that, and I'm a good example of a person who rarely bothers with coupons if I'm already buying it. But in that case it takes pretty substantial effort to use the coupon. You have to keep track of it, often it's good for a specific time frame in the future....those coupons are a real pain. But Amazon coupons, where you just check the box? I use it every time it's offered. Whatever the entity is getting or learning from my use of coupons on Amazon is very different from usage in real life, and seems like a negligible gain.