To accomplish a certain coding work, guys would work on it day in and day out non-stop.....I just never met a female that would do the same as a programmer.
That's because they have a life :-D. Seriously though, I think the reason why you don't see many female programmers is because computers in general are seen as boys toys. I only became a programmer because I was interested in computer games as a kid - most girls didn't play computer games when I was a kid and this is the end result.