So I feel like there are two main kinds of fandom, two main ways in which people express themselves fannishly. There's what I tend to think of as "text-centric" fandom, the kind that I tend to associate with old-school, male-dominated sci-fi circles; an obsession with the minutae of the spaceships, the languages, the worlds and their climates and populations, the details of the story itself. This kind of fandom likes to catalogue, likes to be completist, likes to be correct on its details rather than exploring what-ifs. In fandoms that don't have sciencey details to obsess over, it's often characterised by a heavy focus on what's canonical and what can be deduced from the details given in the series. It may involve emotional attachment, but that emotion often isn't expressed too fervently; people tend not to gush.
Then there's what I call "character-centric" fandom, where people get excited about the characters as people (or concepts of people), and like to play around and be creative with what those people might do in situation X or Y. This is, overwhelmingly, the type of fandom that inspires fanworks; the type of fandom that writes fics, that draws art, that slashes and pairs, that writes speculative essays, that makes vids and colourbars and generates other expressions of, well, fannish love.
What sets these two kinds of fandoms apart, I think, is that one treats the characters, as aforementioned, as people, and the worlds as worlds, and the other treats them as fictions, as documents set in stone. Where one type of fandom is willing to look at a character and wonder what they might have been like if this or that event in their life had gone differently, or speculate on their emotional reactions to a certain thing, the other type isn't deeply concerned about anything that didn't happen in the canonical series. It's happy to analyse the text as literature, but being literature, it is treated as something that it makes no sense to be creative about; what's there is there. Character-centric fandom often also recognises the literary value of a text, but doesn't see this as a limitation to conceptualising the people and worlds involved as if they were living and breathing.
I've theorised a couple of things based on this:
* The overall dynamic of a fandom - the driving force behind it, regardless of what individual fans are doing - sems to differ depending on how easy it is to make fannishness in that fandom a socially bonding activity. TV show fandoms, even if they're fairly small, seem to generate a lot of character fannishness because their weekly schedule makes them a talking point and thus invites more bonding between fans than a standalone text that people are discovering at different times. Videogame fandoms, while small, seem to stay text-centric until a certain critical mass of people is drawn to the fandom, at which point they become character-centric fandoms. (Witness old-school versus current FF7 fandom for possibly the best example of this ever. Or worst, depending on your standpoint.) In general, the bulk of the character-centric collective becomes drawn to a series when it becomes popular enough that they can emotionally connect about it with other people.
I may be a little off centre here, but I think I'm observing at least some kind of trend, even if it isn't quite the one I think I'm observing.
* Fandoms that are text-centric don't get it when people with a character-centric view of fannishness come in and try to be fannish.
Essentially, the purpose of fanworks seems to go over their heads a little. I found this out when I tried to write slash in the Lunar fandom; the entirety of the fandom just seemed to take a collective look at me and go, "uh, what". It wasn't that they were for it or against it; they just didn't have the ability to parse it because it wasn't the way they interacted with the series.
And here's the thing. I tend to be someone who gets into small videogame fandoms and wants to interact with them in a character-obsessive way. And it goes completely over everyone else's heads. And I think I'm just beginning to understand why. It's partly because they don't have the familiarity with the semiotics of character-centric fandom; they're not used to seeing fanvids, crackfics, and all the rest of it, and thus they don't have an immediate template from which to relate to them, but have to understand them from scratch. But I think it's partly also that this just isn't the way they are fannish, and it never occurred to them that fannishness might be this way for some people.