It's not really too complicated.
How come there use to be almost no male nurses? Or homemakers? Or elementary school teachers? Because society said that men didn't do those things. Now of course times are changing.
But the same thing is with magic and women. You turn on TV... it's always a male magician. Criss Angel, David Blaine, The Masked Magician, Jeff McBride, Copperfield, Penn and Teller, etc. If you do see a girl, she is nothing but eye candy for the audience. Ironically she is usually the one doing the "magic" but I won't get into that.
The point is society said girls aren't magicians, they are assistants, if anything.
Luckily though I think times are changing, especially since there seem to actually be quite a few girls on this forum to begin with.
Just give it time... my guess is within the next 15 years, 20% of all magicians will be females, as societies gender roles seem to be meshing together more and more every day.
Katie