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 carts", but in a busy store that cart can be cycles 5-10 times a day so this abuse adds up.
Then, watch the carts get returned to the front of the store. The handler pulls out a 40' long 'cart snake' that is unwieldly and heavy. You'll watch them drag the entire line sideways at points to get it in line with traveling the right direction and to line up with the return lines. Getting dragged sideways both wears flat spots in the wheels and it can bend the castors or pop the soft part of the wheel of its rim.