This article doesn't seem to actually answer the question well... If you want to see the problem, watch carts being put in the cart storage pens and watch carts being returned from those pens to the store. A very small percentage of the carts will end up in pens off kilter, then pushed in by the entire line of carts behind them. This bit of pressure can bend the wheel attachment. Now you say "this is only one or two…
This may be an American problem. In the UK and many European countries, shopping carts ("trolleys") have castors on all four wheels; they will quite happily glide sideways. This makes them more maneuverable in the smaller stores, at the cost of being more difficult to control - more like the ship in Asteroids than a go-kart.