> If a cart always costs 50 cents and there is no hope of ever getting that money back, then: The monetary incentive to return the cart doesn't exist

The grandparent post is just talking about incentives.

I guess what you're saying is that if you pay 50 cents for the bathroom then there's no actual incentive to keep it clean because the 50 cents is gone either way, unlike a cart deposit?

You're probably right about that, but I also don't think most people actually need an incentive not to make a huge mess. I would put money that most messes in public bathrooms are caused by the people that the 50 cent charge filters out. The rest experience some social pressure from the attendant to keep things clean. If all else fails, the attendant can clean up a mess before the next person uses it