For a while I used to think larry david hated us. No black recurring characters in seinfeld and then for like the first few seasons of curb your enthusiasm there weren't any black recurring characters.
I'm certain the people behind these shows:
How you gonna set a show in one of the most multicultural cities on earth and have an all white cast with no recurring black characters?
Also with some of the actors in those shows, I don't think I've seen them in TV shows or movies where they have a black co star(e.g. Neil Patrick Harris, Matt leblanc, Jason Segal, Sarah Jessica Parker) could be wrong though.