Their job is already to gather carts from the corrals. Putting carts in the corrals allows employees to gather carts if they enjoy it without it being an extra inconvenience if they have a time limit. Also like 99% of employees would say they dislike people who leave carts everywhere, especially when they, you know, are a threat to cars if they roll into someone's vehicles, hence why cart corrals are a thing in the first place. I certainly don't want carts taking up parking spaces or rolling into my car if it gets windy.