We have now this in Migros and Coop:

Place it in the stack at the checkout where you unload it and go. Kinda breaks that test. And a headache less for the clerks.

Another possibility is that people that don't return the cart may not be having their needs met. A person who is tired after walking across the hot parking lot may not return it out of a desire to maintain a modicum of health. Or, perhaps, they may not think about it because their cognition is temporarily hindered by hunger, exhaustion, or some other carnal need.

On Maslow's hierarchy, I'd say if a person meets all of their physiological and safety needs they are more likely to return the cart than those who do not.

slight flaw in this theory, I always return the cart and will often return other carts as well. despite this, I am terrible at self governing to the point of nearly failing out of college. that being said return your carts you bastards

I return mine because its an opportunity to get more steps in.

After taking it outside boundaries so a wheel locks up.

Look at tge people returning them in the lot, mostly fat and/or wealthy.

In my country we have dedicated people in the parking who literally follow you, can even push and collect the cart from you.