The best of us will put our trash to the curb with care, but animals or the trash collectors might make a mess despite our efforts. So I pick up what I can. I rake my 93 year old neighbor's leaves because if they are left on his lawn, they blow to mine, it's less about doing him a favour - more about my OCD.
When I was a 15 year old kid working at a Chevron gas station, I found that if the washrooms (especially the women's) were kept clean, they stayed clean. Let them get a bit dirty = all heck broke loose! I think your neighborhoods are the same sort of thing, so keep picking up.