I'm not sure I agree with the premise, but Randall Kennedy gives a good explanation of Obama's popularity with African Americans:
First, Obama has delivered on what most blacks most craved: a serious, competent, dignified male politician who identifies as black, is married to a black woman, is free of any associations understood as anti-black and is simultaneously attractive to enough whites and others to prevail electorally. It is difficult to exaggerate African-Americans’ frustration with the stereotype of black male irresponsibility or their yearning for a dramatic counter-image. Obama is the antithesis of The Black Man as Failure. That alone buys him a lot of gratitude.