I understand your point about setting and world building/exploration, but I'd have thought the allure of writing for main characters is brazenly and unmistakably obvious, and fertile ground for writers; it's to explore these characters in ways the official canon doesn't.bastardofmelbourne said:That said, I've never understood the point of fanfiction that's written with the main characters within the plot of the actual source fiction. Like Buffy fanfiction. I don't get into it because as far as I care, it's not going to replace the show and the fact that it's trying to is working against it.
If someone's intrigued by a certain character trait or dynamic between characters, but they see these aspects aren't explored either at all or to their fullest potential, then you write to do it yourself. All fanfic is a reaction to what's there, and so writing for main characters is arguably the purest and most 'reactive' approach to take. People didn't stay with Buffy and co for seven (or more) seasons for the world, they stayed for the characters inhabiting that world.
I've only written bits and pieces for established IP's since adolescence, and only one complete piece in the last five to ten years I think, but one unfinished/barely started piece was actually featuring Buffy, and Faith. Yes, yes, writing Buffy/Faith slash is about as inventive as Mulder/Scully... but some pairings are like veritable lightning rods for good dramatic [and/or erotic] reason.
Buffy The Vampire Slayer never explored the not-so-sub-subtext between the two Slayers, and had it done so in Season 3 it'd have pretty much dragged the entire arc off track (in an already busy and arguably initially quite disjointed season). There wasn't room or time - or a need (Faith was, with all of BtVS's characters, a cog in the wheel of the themes pertaining to Buffy Summers herself) - to explore it.
That's where non-canon writers come in, to take what could've been and explore it. It doesn't seek to alter, expand, or "replace" anything about the core IP. I tend to think of good fanfic as a kind of alt-universe dialogue between the fans, the creators, and the characters - who ostensibly belong to both creators and consumers.
edit - to briefly elaborate on writing for Buffy, for example; how would she deal with a given arc? And how would the Scoobies react? And what would those reactions reveal about these characters and therefore the universe Whedon and co created? A simple concept of a story leads on to ripple effects which then explore far more than just the lightning-rod leads themselves.