I can only speak for myself and pretend to speak for others like myself
Someone asked me about this at Writer's Weekend about why there aren't more minority writers being published in sf/f. I think some of it has to do with the interest as well as the whole minority thing.
That is to say, those with Asian-American backgrounds (such as myself) tend to not be steered towards the arts as a potential career or hobby, at least to the extent in which one would give up other things in the drive to get published. Since it's neither stable nor lucrative it is a waste of time, as it were. (Though there is some leeway for Important Literary Stuff, but not so much sf/f.) I have a lot of other Asian friends involved in fandom and such, but not at a point in which they really, really go for the dream as it were. It's just a fun hobby to write fanfic or whatever.
So, if you've got a minority, and within the minority is even a further minority who is interested in chasing the dream, and then add the steep scale of even getting published and/or being successful no matter what your minority or majority and... well, not many break through.
But then not many white folks do, either :)
At least, that's my take on the Asian-American experience, but please feel free to add or correct me. This is just what I've gone through and seen others around me go through.