What is the fundamental reason behind this phenomenon?
Because they view it as nerdy, which is also why some girls who follow trends, geek being an in trend right now, have latched onto gaming. You know the ones, they wear frames, and if questioned if they like games they will say how they love mario and zelda, despite not knowing anything about it. Also look out for triforce tattoos or space invader tattoos.
Serious answer, IMO: I was able to get some female friends into gaming when I was young. Only difference it seemed, between them and me, was that when growing up, when not neglected, the interest that was taken in me was steering me towards more stereotypically male activities, like fishing and golf and going to football games, which stuck with me to this day. Games were a great electronic babysitter, kept me quiet and out of the way, so that was one thing I was given fairly generously. Female friends were pushed in other directions I think, even if their parents didn't consciously do so.
In my case a part of it might just have been natural inclination-- I was always attracted to gadgets of all sorts, anything with buttons, from a very young age-- but I really think more women would be into them if introduced while young and encouraged to play.