This is because they are told they are supposed to act that way.
I could rant for days on this subject. Most of the time, the things we observe have little to do with color. They have everything to do with upbringing, the lack thereof, and institutionalizing what is deemed popular or "culturally" acceptable. Has nothing to do with skin color. Has everything to do with stupid.
Look at the way some certain congressmen and women act. They have a club all for themselves only for people who look like them. What do they do? Sit around being black together.
When one (allen west) breaks away from the group and exercises/illustrates independent thought and opinion, we are told he is "uncle tom" and he's not "black enough". Who exactly are the racists here?!