* Yes, it's the "right" thing to put your cart back. It's often 10 seconds. That being said, there are cases where I have my daughters in the car on a hot day and don't want to take any risk with stepping away. Find a safe, stable place for that cart to ride out the heat and ensure my human companions don't have any risk.
* The cart person is going to round the parking lot no matter what. Even more, there's a good chance it's a high schooler who doesn't give two craps whether they're grabbing carts from the parking lot or stocking shelves. They're getting paid near minimum wage to do a minimum effort job.