Democrats are NOT incentivized for Black Americans to do better. Democrats rely on the victimization of their voters. If their voters are no longer victims, democrats' jobs become much harder.
If democrats can keep Black Americans thinking racism is a huge problem in the country, it's a very effective way to keep black votes. If black people keep struggling, this actually benefits dems as well because they can blame it on history, racism and the past.
Which then allows democrats to continue to paint themselves as the ones who will fix these "problems'.