From the Civil War until the 1950's, blacks overwhelmingly voted for Republicans by about a 90-10 margin, because the GOP stood for race-neutral rules and equality. (Southern Democrats were the source of Jim Crow laws, the KKK, and segregation.) From the 1960's on, the Democrats switched gears, and decided that they would continue to support racially-divisive laws, but now only those that favored minorities. Now blacks vote for Democrats by a 90-10 margin.
Apparently, 80% of blacks have 'principles' that are easily bought, or are more interested in racial preferences that FAVOR them rather than in equlaity for all Americans, as they used to pretend.