... OK, I'll bite at the troll -- and I have not stopped beating my wife.
First, just how many women do you expect? Looking a closed-source companies is a bad comparison since all the large ones are under a form of voluntary "Affirmative Action". Defensively against lawsuits, they try to hire according to the source population (college grad) gender numbers. I know, I've done it.
Second, why do you think "open source" is all warm'n'fuzzy, kinder, gentler? I know, I've done that too -- both run a project and tried to get kernel patches accepted. F/OS is _ruthlessly_ competitive and heavily slanted towards negative feedback when you are lucky enough to get any. For good reason, the kernel maintainers are busy and justifiably concerned about code overgrowth. You have to like beating your head against the wall. And then hit just the right problem with just the right code at just the right time to get in. Get lucky a few times, and you get more attention. But its a dogged uphill battle. Perhaps not one many women [egalitairian, risk averse] are motivated to engage. But how or why should it be otherwise? Please tell. IS F/OS short of development? Would the instability of greater development be an improvment?
Finally, the only time gender is a legitimate inquiry, sexual orientation is equally important. Is there any evidence the F/OS is homophobic, racist or discriminates on other axes? Then why assume it discriminates just because there are few women?