It seems to be different in the USA, but here they wouldn't. If somebody would abandon a shopping cart, it would stay there indefinitely until somebody returns it. I mean the employee might do it after work, on there way home, but also only for the same reason any other random person would do it.
They are getting the carts either way. No one is saying to return all carts to the store. There are several partking lot racks for a reason.