The shopping centre where I shop frequently (Europe) has a large outdoor parking space and every 20 meters or so there's a little kiosk where you can return the cart. People do because it's actually easier to return it than to worry about crashing into it when you're getting out of the parking spot. From time to time an employee goes out and collects all the carts from kiosks and gets them back to the shop. I don't know if it's the same way in the US, maybe some people don't return it simply because they parked too far from the entrance.
Not so much a kiosk, but American grocery stores often have one parking spot every other row that is blocked off with a fence/barrier and marked as a cart return storage. But that has its own problems because if someone hastily shoves a cart in there instead of stacking them in line it takes up too much space and creates a dangerous extrusion into the adjacent spots.
This is certainly useful as a one-time reveal since the attackers didn't think this data would leak, but now can't they prepare better?