Why are sidewalks so clean in Korea?

Every now and then I see someone on YouTube wonder how it can be that the streets and sidewalks here in Korea are so clean while there are no public trashcans available. The secret is: Old people.

Let me explain, every morning when I go to the daycare with my son I see between 5 and 10 elderly people walk along the street with their yellow vests - which say "Pangyo Senior Welfare Center" on their back - and pick up all the trash. I guess this is some kind of a thing they do to keep them engaged and moving.