Single White women are, presumably for those of them who still have a bit of bloom on the rose, actively trawling the sexual market for cad and cavalier. Thus, they are in their stage of life when all faculties, mental, emotional, libidinal, are focused to a pinpoint of estrogenic vitality, with the familiar shit-testing behavioral profile that vitality presupposes.
Also, as mentioned later in the post, for many single, white women it's about virtue-signalling. Look! I'm so open-minded and totally not a racist. I looove colored people!