I don't get where the confusion lies.
I have a coupon for a specific item. I think to myself, "Hey, I need that item, think I will go buy it and save some money to boot." I buy the item, use the coupon, then realize "Oops, I already have plenty of this item", or "Oops, I forgot I actually don't like this brand, think I will return it".
So I return it and I get back what I paid. Why would I need the coupon back if I do not need the item? I already bought it and saved the money. Then I decided I did not want and/or need the item, so therefore I DO NOT NEED THE COUPON. I am NOT entitled to get money back that I did not spend if I did not keep the product.
Coupons are not gift cards. They are a discount on a SPECIFIC item.