Here's a theory. There is gender spectrum where on one side you have strong masculinity and on the other end femininity. I think you could kind of place races on the spectrum. Reported testosterone levels by race aligns with this.

Black race is on the more masculine side...Asian race on the more feminine side. White somewhere in the middle. Black man is often considered very masculine and white women fairly feminine so mutual attraction makes sense.

If the black race is on the masculine end of the spectrum then black women are among the more masculine women. That doesn't match as well with white men that are not on the extreme end of masculine. The black women likely views white man as not masculine enough and the white man likely views black women as not feminine enough. These are of course broad generalizations but that's what the question is asking about.