This is a bit rambly, and I'm sorry. My original somehow disappeared when posting last week's post, so it's re-written from notes and not as edited as I like to be.
But here's the thing with miniatures games: they require a great deal of solo effort to paint and assemble the pieces. In my experience, there tend be a higher percentage of introverts among miniatures gamers than among the other segments of the gaming populace. In fact, I know people with sizable miniature armies who have never played a game. They love collecting and painting.
It's this solo part of the hobby that I suspect is responsible for the reputation that the rest of the hobby has been painted with. It applies less to boardgamers, but we are still colored by it, reputation-wise. It requires a great deal of focus and dedication - I know that when I'm doing detail work for one of my minis, I tend to tune out the rest of the world.
Something I don't want to overstate, here: Social aspects of tournament play.
I've participated in and run tournaments for a very long time. And much of "gaming as social activity" goes out the window for tournament play. Because those people are there to win. There are exceptions. And it varies widely, depending on the game and number of players. A 7 Wonders tournament will be more sociable than a Hordes tournament. It's because of the in-game interaction. In a Hordes game, you'll be in a series of one-on-one matches. The only people you'll interact with at the table are direct foes. In a 7 Wonders tournament, while you're competing with up to six other players at a time, only the players to your left and right have the ability to directly effect your winning or not, so you're free to be friendly with the other players at the table. And most players have a difficult time being friendly to some strangers and not others. But then, a 7 Wonders tournament with tables of three or four will be more cutthroat.
And then there are games for which the social is the point of the game, whether it be a negotiation game like Diplomacy (where your social skills are a significant and important part of the game) or a word-association game like Apples to Apples (where the "game" itself is pretty thin).
One last thought: A lack of desire to be sociable does not necessarily indicate a lack of social skills. If left to my own devices, I am often (still) a chair-dwelling basement troll. But I apparently have reasonable social skills, because I keep going to conventions as a demo monkey. And being a demo monkey is 100% about your ability to convey the fun of a game to a prospective customer.