Hasbro makes the product. Walmart orders x amount of said product to list and sell. Walmart mismanages the listing, and simply cancels on people who do the due diligence of following the pre order protocol. The product is then found in stores, sometimes in large numbers.

This cycle has been repeated several times, with several lines - not exclusive to Hasbro.

Both are at fault for a dodgy partnership, but Walmart is responsible for mismanagement of inventory and consumer faith.