Also, most those large stores just outside of town have vast parking lots, enough so that I bet that a lot of people would decide that it's not worth $0.25 to take the cart all the way back to the building.

In denser cities where it's just not practical to put your supermarkets impractically far away from literally anyone who might sometimes want to buy some food, what you typically see is some sort of system where the wheels automatically lock up if you try to take the cart outside the parking lot. Which, compared to the Aldi system, always seemed to me like a $10 solution to a $0.10 problem.