Maybe that's not so much a problem in the US, where I imagine supermarkets may not be in the city center but mostly reachable by car and thus less foot traffic to take the carts?
But maybe the deposit here in Europe is just silly? I do know many supermarkets lock their carts up for 1st of May for example and anyway, one euro or one of those plastic discs is not hard to come by, so it is not much of a detriment.