This is my fear.
You're working a job. You're expected to be working during your shift. If I save you a few moments by returning my cart correctly or stacking carts in the corral, then I'm not actually saving you any time, because all I've done is move the next task closer.
The flip side is something like the movie theater floor cleaner: If I throw my popcorn everywhere, then that person has a job. If I'm tidy and don't make a mess, that job might go away or the staffing for it cut.
My hope is that by reducing the need for the unskilled jobs of cart cowboy or floor sweeper, then we build more skilled people. But I also recognize the need for unskilled jobs because no one starts out with a professional background.
I return my cart because it feels right... but is it?