Whilst I put my trolley away, due to leaving it lying around causing obstruction, I can't really blame folk for not putting them away. That's what checkout and trolley monkeys are paid for.
At a restuarant, do you take your plate back? No, 'cos that's someone's job to do it for you. Customer service and all that. Next time you see a trolley lying unattended, be a dear and put it away. It's your job afetr all. Seriously.