The store purchased the item from the manufacturer. The manufacturer "buys back" the the unsold inventory, through an MSC.There can be several reasons for this, but usually it has to do with meeting a sales volume required for the store to purchase more items from the manufacturer. For example, the contract may specify if 80% of the inventory sells within 60 days, the store is committed to another, possibly larger, purchase. Less than the specified amount, the store does not have to purchase again.
Other cases are when the manufacturer makes a deal with the store to wholesale for a steep discount, with a caveat if enough volume sells, the store pays the normal wholesale price.
In both cases, the onus is usually entirely on the manufacturer to market their product. This usually happens with newer products. When regular sales are not enough to trigger clauses requiring additional purchases or bigger payments, the manufacturer may do a buy back to make it happen.
Buybacks usually come with instructions that you absolutely cannot return the items and may want proof that you've destroyed the packaging of obscured the UPC. You may also be encouraged to give away the product to as a form of marketing.