I think there is a high barrier to entry into the film industry for women and minorities due to the fact that much of past film has been dominated by white men. Originally, I didn't completely believe this because I have an internal locus of control (I believe that success is earned, not just given [although I do also believe that having the right connections sets you far ahead of the competition]; therefore, being a woman or minority is no excuse for lack of skill and success). However, I now believe that because society has become so accustomed to seeing a certain type of movie (hence the predominance of white men in the film industry in the past), it is more likely producers will want to hire those (white men) that have proven to been most successful in the past.
My point being that if one invests in a production, he or she wants the highest probability that his or her money will be increased. Since white men have shown to be most successful in the film industry in the past, it seems only logical that they would want white men in their production.
Just in case I wasn't clear enough, I do not believe that race or gender (or both) should be a determining factor in the choosing of members for a production (or anything else); it should all be based off of skills and ability.