If I had to guess, I'd say it's something between just The Nature of The Beast - people often start things, join clubs, enter forums, and wind up not sticking around because they forget to come back, or life gets busy, or something else comes up, and I think that happens to a lot of things and a lot of people. But also, we... do have an unorthodox sort of forum here, and I do think people get thrown off by that. (This is not an invitation to start debating about The 'Board vs. a hypothetical T-Board again, or what have you.) But this 'Board is very unique, in this day and age, and I've noticed a lot of newbies comment on their confusion at it. I wouldn't be surprised if that's part of the issue some people have.
Other than that, I guess, what other people have said - we wind up not being what they expect, for whatever reason. Either we're too serious, or we take writing too seriously, or we're too off-the-walls, or they expected to get Permission and be having madcap adventures or Serious Grimdark adventures, and that didn't work out.
I don't think you're scary, hS. You do... loom, a bit. You did when I was a newbie, anyway - now, either I've grown a tolerance for looming, or I've grown, without realizing it. I've been accused of speaking, IRL, as if I always know the answer, or am convinced of my accuracy on a subject, and told it comes off as authoritative/arrogant. I think online, when one speaks with both intelligence and a measure of confidence, people sometimes get the idea that this person should not be argued with, and you get the impression of looming, instead of arrogance.
(I really, really hope that came off as friendly offering of explanation, rather than snapping-turtle critique, because it really is just friendly observation and I do not think of you as arrogant at all.)
Anyway. Questions.
1)
Well, it was recommended to me by someone who had taught me the basics of Elizabethan grammar, and was a brilliant writer and mod who was slightly notorious for her high grammatical standards. I'd read the Original Series, exchanged a single e-mail with Jay about permission, and enjoyed OFUM. So I suppose that was the community I was looking for - good writers, with high standards for their writing and canon, and a healthy dose of humor and friendliness. And, more or less, that's what you were. And are still, I think, for the most part.
2)
Once or twice, I'm sure. For most of the past eight years, though, I've checked the 'Board either daily or close to it, reading topics that catch my eye and skimming everything else. There were a few nasty drama flare-ups, multiple years ago, when I made the decision to leave, at least for a few months. Every single time, I found myself checking the 'Board daily -anyway-, because I'd formed the strong habit, and the URL was ingrained in my muscle memory. (I never wanted to leave permanently because Dann was here, and I couldn't get up the nerve to talk to him outside of a PPC context.)
So I guess that would be it. Drama has made me think about drifting away, or setting distances, but so many of my friends are here - this is like a home, I never could.
3)
I guess I answered that one up front? I don't know why, not really. I see people drift in and out of forums all the time, and the IRC, where I'm more vocal, seems to have a core of regulars that's grown quite a bit, and it's slow-growth these days, but we get new people still, who come in every few days and stick around.