Trash Can’s in Los Angeles

Trash Cans
Why are the Recycling trash cans the biggest trash can’s? The black trash can’s are the smallest out of the three trash cans. I guess when you are mowing your lawn or pulling the weeds, that gets a lot of Mulch. At my house we have Two black trash can’s, two green trash can’s and one blue trash can. But the black one is still the smallest one, i don’t get it.