Oddly enough, I Goggled the subject, and I am not alone, others have written on the same subject.
Best answer, "I had my kids in the car and could not leave them." "I was just too tired to walk all that way back." "It was raining too hard." "My Mom never did and neither do I."
My theory, you are "borrowing" the cart, and it should be taken back to where it came from. If you borrow something you should take it back.
I generally, if one is nearby, or if one is standing, all alone, in the lot, I push it into the store and use it, fill it up with groceries, wheel them to my car, and, when done, place it into the "done using it corral."
After an extensive survey, done by myself, women are more inclined to leave their carts in the parking lot, I think. Men look longer for a "good" parking spot.
Why don't ALL "parking lot cart picker uppers" wear reflective vests? All of Walmart's do, some other stores don't.
Differtne names at different stores .... shopping cart pusher, mule, cart mover, cart puller, cart retriever, trolley mule, or even a shopping cart collector.
One store that I know of is smart. You have to put a quarter in to get a cart, and take it back to get your quarter back. I noticed in the East, intentionally or not, there are just enough carts to go around. Incoming customers see one in the lot and take it in with them, they never sit in the lot long, smart.
That is more than anyone needs to know about parking lots.
