None of those girls are necessarily anti-interracial, it's promotion. Their managers tell them to hold off on it for now. To keep people interested they have to slowly do more and more things. That way girls can start out only doing girl/girl, build up interest, then start fucking men but not taking facials, then fucking men and taking facials but not doing anal, then fucking men and doing facials and anal etc. If they started out doing everything, you'd lose interest quickly.
It's dumb that doing the same thing with a black guy that you've already done with 100 white guys is considered more dirty, but it has to do with how fucked people (americans particularly) are about race. Czech pornstars don't seem to give a fuck but American girls all want to follow Jenna Jameson's career path and she never fucked black guys on camera (at least as far as I know).
I don't care one way or another (as long as it isn't lee stone), I'm not looking at the guy.