Why no y?

Interesting read on pinkbike entitled "why no y?" about the lack of females in mountain biking.  I think its funny that the author mentions surfing like I did in the post the other day.

But I feel like way more girls ride MTBs than BMX even.  Is it because these sports are center around dudes, or catered to dudes, or do we (guys) just naturally gravtitate toward more physical activity like biking, while something like surfing isn't as physically demanding?

And are girls just supposed to sit around and do their hair or paint they're nails all day instead?  Is it society setting up standards for what genders are "supposed" to do or do different genders naturally go towards these things?  I'm not sure anyone will ever figure out the answers to those, but all I know is I want more girls to ride bikes.  Especially ones like this...