Having two sisters that date/marry only white men, and a mother that, in the past, frequently cheated on my father with white men, I have some theories. I find that, although many bw attempt to discredit relationships between black men and white women, the main issue is projection. Black men and white women have actual intersectionality. We both suffer at the hands of the opposite sex within our respective races, and we are both trying to push past it. White women that realize this, tend to make for great and solid relationships as friends or more. In the case of black women, they project their own feelings of inadequacy and their own want for white male acceptance onto us. So, the assumption is, "oh, you just want white women because you want their approval, or you think they will look at you like your better than a white man". The reality is that this is a projection of their own insecurities.
I will explain. Poll after poll shows that black women are often considered to be the least desirable women. It's certainly racist and fucked up. It creates a bit of rivalry that has existed since slavery. The rivalry being black women vs. white women. Black women knowing that if they can get the affection of a slave master, it would enable them various opportunities, meanwhile the white wife can't do anything about it. In today's world, the goal is to replace white women as the object of a white man's affection. And it isn't necessarily a product of wanting to be seen as the most beautiful, but a product of wanting to be associated with white male patriarchal power. The goal is to dethrone white women. Meanwhile, the goal for some white men, is to dethrone black men from the pedestal of masculinity. We may not be seen as the most attractive, depending on where you go, but in every country I have ever traveled to, black men are often still seen as "most masculine"/"most feared" which can be good or bad. White men don't have an issue finding women to desire them, but some maintain "cuckold-level" fears of black masculinity. So, they create a rivalry, which is why black man vs. white man in combative sports always sells so well.
These situations provide us with a unique experience that essentially should bring white women and black men closer together. Sometimes it does. In fact, it used to back in 2nd wave feminism. This current wave doesn't. Black Men and White Women should be each other's greatest allies, but, propaganda, current waves of feminism, white supremacy, and black feminism keep us apart. It's a shame really.
Back on subject. This is why representation of black men with white women, in television, film, and overall media is so important.