Many powerful Democrats go out of their way to ensure that their core constituencies never get ahead.
Democrats get their most loyal voters from minorities who feel oppressed and the poor. If there was racial harmony, their monolithic support from the first group would vanish. If there was widespread prosperity, there would be fewer people in the latter group.
The Democrats have a vested interest in keeping racial strife abundant, in spreading proverty and economic despair, and generally spreading misery.
Regards, Ivan