Some people are so busy that they have no time to really take the shopping cart back and put it in the store or in the shopping cart stall outside.
I used to hate it when people would leave their shopping carts outside the store in the parking lot but after having kids I can understand why it happens if they have kids.
After shopping I had to deal with the kids and put them in the car and I could not leave the kids in the car alone to go put a shopping cart away because the store was too far away from the car or the shopping cart stall was too far away as well.
I tried to put the shopping cart away to keep it from hitting someones car etc or I would hand it off to someone.
But the store also has someone that comes out and gets those shopping carts so I don't feel so bad because someone has a job because we leave our shopping carts out.
It can be hard when you have young kids that you cannot leave alone for even a few seconds in the car to put a shopping cart up.
So that I understand but I've also seen some people without kids leave the shopping cart out and for those people they should put the shopping cart away.