If we're looking for a reason, I think this is the best one I've heard so far.
The thing about the media being the cause I think is wrong, that was just an effect.
The cause I think is spot on, that males are competitive and in general more solitary (damn that testosterone), and females are more apt to be concerned with social aspects. In the late 70's and 80s computers became much more accessible to those competitive loners (nerd stereotyping here).
Which is to say, its not that females can't do it, or that males are better at it (insert whatever you want for it), its just that they are quite possibly just not interested as much. Before the advent of Personal Computers, computing was mostly prevalent in an academic setting, which is more social..