That's strange. Mountain Biking was my AA for years. (It didn't work, BTW). There was a definite fellowship, and a common love of things mechanical and of nature, and (of course) going really really fast.
It IS a testosterone driven sport for the most part, and some of the cliques you really have to "prove" yourself to get accepted. Even though showing up on a routine basis, volunteering to help maintain trails, and trying to go fast usually suffices.
If you think Mountain Biking is bad, go find a Criterium after work with the "roadies". The rumors are true, they're snobs. Fast snobs, but snobs.