The most compelling reason I've heard is a converse to the point that one is making the employee work more to get all of the carts. It's true, but (supposedly)

The most compelling reason I've heard is a converse to the point that one is making the employee work more to get all of the carts. It's true, but (supposedly) actually beneficial to the worker. The idea is that working in the store is Bad (essentially because the manager is in the store and the manager makes you do things) and working outside the store is Good because you can work more leisurely even though you have a task to complete. Therefore, being forced to take a long time to gather all of the carts because so many were left outside the corrals is Good. For what it's worth, the idea was introduced to me by someone who claimed to have worked at a grocery store and that their favorite thing to do at that job was to gather the carts because it was so laid-back. I still return my carts but this would 100% be my (honest) justification if I was ever approached by a cart narc after not returning a cart. If only to see their reaction when I say, with a completely straight face and the willingness to argue the point, "This is a kindness." (Also, it's a bit interesting to me that this was not included as a justification in the videos the author watched.)