It's not just grocery stores, it's a lot of retail. Manufacturers of some products literally rent shelf space and provide the product for those shelves. The store doesn't own the product, the manufacturer does. The store just takes a cut of the sale price, provides checkout services, space, attracts customers, etc.

One of the most obvious places this happens is at Home Depot. The tools department is almost entirely manufacturer-rented. If you buy a drill or such and take it apart you'll find that the anti-theft magnetostrictive tag is actually inside the tool, not just stuck on the box!