I think most people who don’t return their carts do so because they don’t see how the action benefits them in that moment. Seeing other carts left in the open only reinforces that. It’s a form of selfishness and disregard for societal norms. Look how many folks wear pajamas to the store or flip flops to sit-down restaurants. Establishing and enforcing dress codes would do wonders once they see they can’t get on a plane or be seated for a meal.
Establishing and enforcing dress codes gave us a society where everyone wore costumes, hiding their true selves. It was a holdover of the Victorian facade.
I for one appreciate having people show me right up front who they think they are.