I blame the lack of emergent gameplay in DF2014 for the downturn. You cannot tell good stories if there is nothing to write about. Yes, DF2014 has a much deeper scope of events, but a titan with over 1000 kills and having destroyed an entire civilization is still a titan, and it doesn't matter when an axe lord lops off its head in one action. Previous versions had consistent large sieges; even if they weren't challenging, it broke the tedium and made for good RP. These days you'd be lucky to get anything larger than 30. We can try to bandaid these problems with mods and challenge rules, but this drives the newcomers away.
My own experience is somewhat tainted by the fact that the forts I ran and was part of were all gimmick based forts that were largely maintained by a single, insular community (MLP forts). As a result, I felt like there has been a lot of burnout among said community, leading to reduced interest in new community forts. Glitterglen was active during a similar period to my first community fort (Dawnpick) and had similar activity levels. Based on some very loose analysis of thread dumps, each of my following games, despite more than a year gap from the previous game, had about half the participation of the previous one. I figured there wasn't any point in trying for a fourth one as a result.
I believe burnout is a big part of it in that community at least, because I was largely recycling players from previous games but didn't have much new stuff to do. By the time Shadytrails came around (my third game), we'd seen it all before repeatedly and there wasn't much point in playing.
However, I'm also pretty sure that the lack of interesting sieges and other conflict was a big part of it too. While we'd done everything else already in Shadytrails, there was never a single ambush or siege, which I'm certain bored a lot of players. Not a whole lot of point in being dwarfed (err, ponied, whatever) as a soldier when you know you won't ever get any action. We did have a couple of were beasts attack, but it's not quite the same I guess, and I believe everyone quit before those happened anyway.
Anecdotally, the forgotten beasts and titans that attacked in Glitterglen and Dawnpick (both 0.31 games) drove a
lot of the interesting story elements in both games. We didn't have many, if any, forgotten beasts in Duskfields (0.34, my second game), although there were sieges. I made up for the lack of titans and forgotten beasts by inventing stuff out of game and using DFHack to insert them manually at the end of the game. In Shadytrails (a 0.41 game) there were neither forgotten beasts nor sieges, and everybody lost interest quickly. The lack of forgotten beasts was a consequence of RP, I guess, since I didn't dig down far in either game.
I'm pretty confident that the ability to go actively looking for trouble in the next version will reinvigorate the community and games. It'll certainly eliminate the lack of interesting events, if someone is so inclined.
Another thing that I might as well toss in is to elaborate on my previous remark that you can try too hard. A big, big problem with Shadytrails, aside from the fact that it was pony related and was never going to attract a wide audience, is that it was kind of the natural conclusion of seeing how far our community could go with the RP heavy forts. Glitterglen was a happy accident there, and Dawnpick kind of got swept up into it. Duskfields was an experiment with a stronger storyline and active plans to make the whole game RP related. Shadytrails took it so far that we were RPing things before the game even started, then dumped pages of text into the first few posts. What kind of new player is going to bother reading all of that to join a game? Evidently almost nobody.
On the other hand, since 2012 we have seen the rise of illustrated games, so this may just be a new form of CGs replacing it. Thoughts?
Interestingly, this was how I intended to run my first fort (Dawnpick) before it accidentally spiraled into a full community game. I'd planned to just post updates with one or two pictures illustrating events that took place.
In my mind it was a way to attract attention with yet more gimmicks, but, really, illustrations are a lot of fun to look at and do make games more interesting. It has a much higher barrier to entry than just writing, so I doubt it'll ever seriously replace conventional community forts or succession games, but as DF gets more exposure and more players, we're bound to see more of them. Plus, those that are done well will probably get more attention because, as I said, it's fun to look at pretty pictures. Nothing wrong with using gimmicks.