>>17688133 (OP)actually goood question
if i have to give an answer is probably due to a mix between upsetting their father and deep rooted racism in them
seeing bleck people as nothing more tahn animals they subconciously developed in them some kind of fetish where the object of hate becomes the object of sexual desire
as for upsetting their father figure they hope that by getting fucked by a bbc their father rejects them and so they can gain the freedom their father denied them