The activist wing was defeated in the primary, and wasn't an option they were presented with. Many blacks are not supportive of the centrist wing and it's devotion to the interests of corporate capital and it near-total-absence of a working-class message, which, when it's the only thing around, makes right-wing economic populism, which does center around working class economic messaging (even if those of us on the progressive side might see it as both an ineffective platform if genuinely pursued, and much of it also a dishonest mirage being dangled as a manipulation strategy), if not exactly attractive—especially when visibly associated with virulent, violent racism—possibly seem the lesser near-term evil.
Edit: according to https://www.vox.com/2020/11/7/21551364/white-trump-voters-20...
Trump gained 4 points each for the black male and female vote, that would put him somewhere around 16, though I’m not sure what that article’s basis was. Still, those are starting from really low numbers to begin with, a lot of it could just be noise.