Not yet, hang on ...
I stick around because I like discussing stuff. I have been on various forums for as long as I can remember and most of those I ended up in the off topic section discussing politics, religion, economy, immigration, terrorism, the lot.
Now the advantage of this place over those other places is, when for instance you have a discussion about , chances are the extremophiles will descend into: "You're a baby murderer", "No, you're a misogynist" territory. While in this place people might call me a coward or a carebear because I prefer a certain game mode. Or a tourist when I don't agree with the direction exploration has taken. Or a Forum Zombie when someone transparently tries to get a rise out of people

In that regard posting here is an enjoyable past time, with the insults limited to the way I play a game (or in this case, don't play a game). Which for all intents and purposes is pretty damn mild and quite easy to chuckle and dismiss. I do find it quite telling that in all the possible motivations you came up with, all of them are negative. Dismissing very obvious motivators. Which in turn intrigues me. What possible motivator could you have to paint me and others like me in that light I wonder.
Besides that, there's quite a few oddball characters here who I enjoy talking to.
And lastly, I have seen this in every gaming forum I am a part off. Gaming forums create communities. The community is larger than the game itself. The community consists of people interactions. Those do not disappear the moment someone stops playing a game.
Oh look! How sweet, a reach around
Tell me dear Ratkatcher. Why should I justify my right to post here? Do I not have that right regardless? How about: "because I like to"?
I'm intrigued