Perhaps they are still discrete ( some are not ) but we see/ know more white woman who are now black only. And many of them married to mature white husbands. These white couples have discovered the pleasures of sex with black men and the wives now enjoy and prefer to be exclusively BBC only. They show no interest in white men but have active sex lives with black men.Sexual fetishism is by definition a sexual fixation on an object or body part regarded as an aid to sexual excitement. I am very cynical with my sexuality and I have no problems to admit that I have a fetish with strong black males and sexual tension with white men has almost disappeared. Maybe because I use to interact with the nerdy or bookish type of Caucasian male in my daily life, and in my most pleasurable sex experiences there was a bbc.
Of course, it does not mean I find all black men attractive... but in general I try to hide this racial bias. Men can understand if you prefer younger or stronger guys, or even if you are lesbian, but a woman that only likes white men is considered racist, and if she only like blacks is considered something worse.