Because of the civil rights Act. It all goes back to that. That got them to switch to democrat and the fear tactics of the black leaders and democrat party have kept the blacks in line since the 60's. There is a real fear in the black community that if Republicans get elected they will institute some racist policies or take away blacks rights. Now if you ask a black what racist policy the Republicans will introduce or what rights they will take away Blacks can't tell you. It doesn't matter though because they believe this is what republicans will do. It's all fear tactics.

Supporting anyone but a democrat is also considering going against your own race in the black community. This is why black conservatives are attacked so much. They are considered race traitors or other garbage.

Blacks have no political power anymore. Any group that votes 90+ for one party has no political power. The republicans don't even try to get the black vote. The democrats never have to do anything for blacks because they vote for them no matter what. As a result blacks are completely ignored. Obama didn't even address the NAACP. Instead he sends Biden. You would think the first black President would address his own people.