Why can't girls be geeks on TV?

Geeks are in, at least judging from the popularity of The Big Bang Theory. But while we enjoy watching the male geeks on TV,  girl geeks are still a pretty rare sight.

The original concept of The Big Bang Theory was the story of three awkward nerd guys and the pretty "real world" girl across the hall. Since then, two new female characters have been introduced: Bernadette and Amy. Both are talented scientists, but neither are exactly what I would call "geeks." They don't understand comic books. They can't play video games, or they play them wrong. We don't see them wanting to wait in line to watch a movie or referencing Game of Thrones in their every day lives. They are highly intelligent, and their presentation as believable, respectable female scientists, who often understand more about what's going on than their male counterpoints, can only be a good thing, especially in a show that features sexism on such a regular basis. But why aren't they allowed to be the other kind of geek? Why is intelligence something that can be shared by both genders, but silly, passionate, fannish behavior a male-only trait? And even the intelligence is something that is often downplayed for "humorous" contrasts between the male and female characters. Bernadette turns into a shouting harpy reminiscent of Howard's mother, while Amy's scenes play her lack of satisfaction with Sheldon and her crush on Penny for laughs. We rarely see them displaying the intelligence or success they originally displayed, and in their personal lives, they seem to have few interests except the guys themselves.

Perhaps the lack of nerdiness is for the best, since we are clearly meant to laugh at, not with, the guy's own nerdy tendencies, and they are often used as an excuse for those characters to behave in horrible, sexist ways. But I wish that we could see nerdy girls somewhere on TV. And, preferably, in a Willow-esque way, where they are like real people, rather than caricatures for us to laugh at.