Sorry for the epic de-rail. I just noticed how huge this post is. Holy Swiss.
I suppose I'll start with pointing out that you're strait up wrong. UESP and TIL do not have the same content. Not by a long shot. They both have books... but that's about it. Even how those books are presented is different. TIL doesn't have gameplay information, but UESP doesn't have any dev comments. UESP's search, while faster than TIL's, is less precise. I can go on listing. They're used for completely different purposes, and I would wager that their user bases (for lore) don't overlap much.
I geuss my question is... why don't they? TIL, from what I can tell, started off as a simple depository for in-game lore books. UESP seems to have had the same original function (judging by the archives of what their old website looked like). USEP also includes a bunch of (often innacurate) synthesis articles, plus gameplay information. TIL has some much better synthesis articles, plus dev comments. Obviously, they're different websites. My question is, why did both of them get started? Why doesn't USEP allow for dev comments to be added (I'm fairly certain that every other fan wiki I've ever been on allows for 'em), or why doesn't TIL add a gameplay section? As you said, these two websites split the lore depository userbase.
Why does TIL have its own forum? Because why not? The community that frequents the Storyboard tends to be more hardcoe and much smaller, so it's a much more personal atmosphere than here. It is also not moderated nearly as heavily. All this means that we can have discussions that we can't have here. People that are banned from these forums, or just don't like coming here, hang out there. I'm assuming that you mean the commentary thread when you say "girl's bathroom," but you'll notice that at least half of that thread isn't commentary at all.
That was an excellent response, and makes perfect sense. Unofficial forums are a neccessary thing when the official forums have strict moderation policies, and are, well, official.
Why Temple Zero? Because fan fiction, no matter how good or how lore-y, doesn't belong on either TIL nor UESP. Or, again, why not? Temple Zero is a group of people playing in the TES sandbox with a certain outlook. And yes, the website proper hasn't been updated since launch. There's new stuff on the forums, and I'm guessing the PGE2 will make it up there eventually. It's an archive, not a blog or something.
But why not just make a "Temple Zero" or "Monkeytruth section?
What I'm saying in those paragraphs is that, 1) redundancy is OK, and 2) none of the websites are redundant. You're saying that Victoria's Secret shouldn't exist because Walmart also sells underwear, and that Victoria's Secret should sell tampons because they're also things ladies buy. The whole line of thought seems 'silly,' to put it mildly.
No, I'm not at all. Victoria's secret offers a specialized service. Walmart's generalized approach doesn't allow them to hire the specialized customer service that I've heard Victoria's Secret is known for, and having tampons at VS would most likely (1) reduce sales of their primary goods for psychological reasons and (2) not move many tampons, as those are a regularly consumed good that most women already have a steady supplier for (just like, say, groceries and shampoo, all of which are often sold in the same location). I get why Wal-Mart hasn't absorbed Victoria's Secret, and why VS doesn't sell tampons. Stores need to find their focus to maintain competative. It's the nature of human economies, and to some extent or another we've seen it since the start of "stores" as a societal institution.
What I don't get is why USEP, TIL, an T0 haven't merged. I tend to get involved in fandoms in vigorous little bursts, and because of this, I've looked at an above-average number of fan communities. In my experience, fansites for obscure topics usually feel the need to merge together. The ES Lore community stands out in my mind as being remarkably... (I still haven't found the proper word) multi-located (?) while being rather small. Just, for example, consider how we're a much smaller group than the regular-strength ES fans, yet they all seem to stick to the BESF, while we're split up on multiple sites.
To take the first part of your question last, the "ultranerds" aren't any more stratified than regular nerds anywhere else on the forums. Some of us know each other better, some of us have histories together, some of us share views, some of us hang out on different forums/sites/chatrooms. On the other hand, there are going to be people who just don't like each other or don't agree with each other's views, because we're all human and that's what humans do. None of that implies cliques or real segregation. This isn't a 80s highschool movie where Proweler, Luagar, and the Word Merchant are giving people wedgies after gym class while MK takes their lunch money. I'm going to interact differently with the aforementioned four because I talk to them often and know then rather well, which might make it seem that we're a clique, but we not a hivemind or set to keep people out. To end with a metaphor, we're as much of a clique as people who play female characters in Skyrim are, or as much as people of Russian descent are.
OK, so, major miscommunication #1: when I said "ultranerds" I meant "all three hundred people who have a personal definition of what CHIM is" not "the people on TIL." I meant it as a uniting term of admitted mutual peculiarity, not some sort of alienating jab.
I also understand why groups of people on these forums would develop relationships. I recall that you and Proweler and a few others were all still active here the last time I was actively involved in the lore forums, years ago. I get the impression that you kept at it, and had been going at it for years and years. If there weren't a whole tangle of interpersonal relationships between all of you after all that time, then I'd have to start with the alienating jabs

. As a matter of fact, I'd say that these forums are actually quite low on real divisive subgroups, especially compared to the more fanatic fangroups I've participated in. At the very least, none of us have anolyzed what the bodily fluids of the Argonians would taste like, and none of us insult eachother by bringing it up all the time. If you don't get the reference, you should be very glad.
In fact, all of you oldies seem very friendly and inclusive. You help people out, try to encourage their interest, and only ever get dismissive when people start actively pushing your buttons. I'd say that there's a bizzare phenomena here where the legacy fellows, the guys like you and Proweler, are actually significantly more mature than the average forumer, and perhaps even the average human. That's why all of this... site devisiveness (?) makes no sense to me. I get why the guys on No Mutants Allowed hide out there, and why the Fallout Community is so split up. There's some deep divides, some bitterness, and some immature, "THIS IS MY SIDE OF THE ROOM" stuff going on that naturaly leads to the development of fractured websites. On the other hand, I don't really see any of that going on in this extended community. To continue my poorly chosen "girls bathroom" metaphor, it's one thing if you find out that people are saying rude things about you where you can't hear it. Once you find out about that, you get offended and that's that. It's a whole other thing when people almost seem to be hiding away completely innocuous comments. That's just puzzling, and when you find out about it, you want to ask why*. Now, you've already done a more than adaquete job of reminding me why non BSF forums are important, what I don't get is why the unofficial sites are so disparate, and why the TIL forums seem so... cloaked**
So, you're not mentally "set to keep people out". That's cool. But why are all the sites kinda set up in such a way that it keeps things apart? Is there a story behind this?
*I have no idea if this is something that you can relate to. I've lived a somewhat strange life, so I'm not sure how well my experiences translate, but this has happened to me several times.
**The link "Storyboard" sounds like it'd contain, y'know, actual storyboards, not a forum, and the "Lore Forum" is mostly dominated by a huge off-topic thread. It's not exactly straight forward.
EDIT: Damned emoticons, always ruining my lists!