The reason for gender-unbalanceness? Often just carelessness
…and the fact that we think that being a man is the norm and women are an exception or a subcategory, just like “Italians”, “green-tea lovers” or “plumbers”.
For an interesting study on this topic, see this summary on the Washington Post about dialogues in movies: It turns out that women speak way less than men. Not because of the lack of heroines, but rather because whenever one adds a less relevant character (such as a shopkeeper), one is inclined to add a “normal” human being, a man (you would not want to add an Italian shopkeeper to your movie unless you had a special reason to do so, would you?).
Seems to be a good reason to ponder about the people we invite to conferences, collected volumes and the like: It might be that we also invite more men than women at first, since men are instinctively felt to be the more normal kind of scholars. For more on this topic, check this post (by me and Malcolm Keating).