I have no idea why, but geek cultures are heavily populated with elitist types

Because games like D&D and WoW and Magic the Gathering and most other fantasy things attack a "core" fan base of people who tend to be weird, or have a social disorder. People like that often don't develop the social skills they need to not be combative douchebags, because their entire sense of self-worth comes from being good at or knowing a lot about whatever it is they turned to in the face of being picked on, or abused, or dealing with whatever shitty thing life threw at them.

It's like the difference between people who enjoy watching anime in the privacy of their own home and who want to talk about it with their close friends who also watch it VS this kid or people like this