[pdonis]

Part of it is probably just the cost of doing one's "duty". Picking up a piece of litter and throwing it in a nearby trash can is a very low cost thing to do, so even if technically the city is supposed to have someone picking up the trash in a public park, an individual who sees some litter can still clean it up with minimal effort.

Filling potholes, OTOH, is a much higher cost thing to do, and so people are more likely to feel that the city should be using the money they have already paid in taxes to do it. (Another aspect is probably also legal risk--if I decide to fill a pothole and do it wrong and someone suffers damage to their car, I might get sued. The city has many ways of mitigating that risk that I, as an individual, do not.)