Or because people in the community have pride in the community. One of the differences I've noticed between Hawaii and Tahiti is in how dirty and messed up the buildings and streets are. In Hawaii there's more of a "community spirit" that tends to encourage cleanliness. I felt more despair from Tahiti.
Community spirit is cleanliness but also freedom. In a community spirit place you get no litter but you also get lots of artsy decorations and weird spaces. In a conformist place you get no litter and whatever type of building billionaires make money from.