Hruminations: Personal Grocery Carts

Why do grocery stores complain about people using their grocery carts to get purchases home when they are on foot, but don't sell grocery carts at the store? Acme Mercantile, for example, sells an inexpensive cart in Ann Arbor. There are various other models although none exhibit the design of the jogger's stroller. It would be nice if one of these manufacturers developed a jogger's shopping cart! Most of the personal grocery carts I've seen are the old pull-style, but there are a few that are designed to be pushed. All of these seem to have wheels that are too small for Michigan sidewalks.