Seriously stop make these accusations without any proof. Where is the hostility? Just because there are a lot of white males™ doesn't mean there is hostility against other people.
by hostility, it seems that you actually mean "Why do blacks and women represent a minority in computer science?"
Computer science has always been an inbetween between engineering and hard sciences--because of that many laymen were employed to do menial computer tasks early in history. This was, perhaps , one of the first chances for laymen to jump onto a scientific industry which turned out to be semi-permanent.
Since we know that education paved the way for the empowerment of minorities, could it be that the statistics that you're referencing are really just moving as a function of women becoming wider dispersed and accepted within all sciences, rather than just the engineering ones?
Perhaps the statistical anomaly that you cite is really a glimmer of hope for women. Computer science is not the only field that readily accepts them now-a-days, and perhaps those numbers actually indicate a migration across a wider array of science and engineering fields that were not at one time available for them, rather than a disappearance of women all together in STEM.
Honestly though, that's irrelevant because WHERE they're going is not what I'm addressing. It's WHY, and HOW can we reverse the trend of anti-diversification in the computer industry? If they're leaving for other industries, even scientific ones, there's nothing wrong with the individuals choice but there's something less-desirable about the computer industry, and I doubt it has anything to do with the raw content of a computer related job.
I'm a big fan of doing things to improve the gender and racial balance of my industry, but I'm not at all convinced that it's actually getting worse instead of better.