I don't read Fan Fiction at all - mainly because when I have checked out what has been recommended, the material seems to be largely reactionary and conservative (in the narrative sense) - if you aren't constraited by the need to have a financially successful product - why put yourself in such a small box?
Because it still needs to be successful in terms of readership and, unlike you obviously, most people that are inclined to read Trek fanfic want to read new stories from that small box, and will declare anything from outside of it "not Star Trek." It's about knowing your target audience. If I want to do something outside the Star Trek box, I don't write Star Trek.
Some people have very specific personal preferences for ST fanfic. I've been discovering my own, by reading scads of what's online and recalling what originally drew me to the physical fanzines I own.
I've discovered that most slash stories make me feel queasy. I'm not homophobic; I have enjoyed some slash stories... but they had to be written for more reason than "I'm gonna write a Star Trek story where two guys have sex!" They need to be
in character and a reasonable part of the plot. They also need to be not too explicit.
So I could enjoy a Garak/Bashir story since those two characters had subtext all over the place throughout DS9's run. Some fanzine authors wrote Sulu as bisexual, so it was reasonable for him to enjoy relationships with women and/or men.
But Kirk/Spock? Just... no. I honestly cannot fathom any circumstance where those two characters would seek a sexual relationship with each other. So I avoid those stories. They're the ones that tend to make me queasy when I read the descriptions of them, and the few I've actually read over the years. Just not my cup of tea at all.
I once got into an argument with a fellow con attendee back in the '80s. She was staring at a copy of
In A Different Reality in utter disgust, ranting about how it "just wasn't Star Trek" for Spock to marry a fellow officer! Well, I read the series of stories where that relationship developed (over a period of several years) and in addition to the undeniable fact that Spock and Ruth loved each other, Spock would - like Sarek - be able to later claim that "it was the logical thing to do." When the reader takes into consideration that Spock's new wife was a scientist, musician, and telepathic... yes, it was logical.
Why does it need to be successful in terms of readership?
Because nobody wants to write something that nobody ever reads. That's kinda like asking, "If you're not going to sell that painting for money, why bother making it look good?" Uh, because I want it to and I want the people who see it to enjoy it.
The painting might be for your mother. If so, you'd make it something she would enjoy, right? That's an example of knowing your target audience, even though you're not making money.
There's a saying: If something is worth doing at all, it's worth doing
well. Even if
nobody else ever reads it, why not make it the best story you can? This world would be a lot poorer culture-wise if people only did a good job on things they expected to be paid for.
Don't most fan fic writers write, first and foremost, to their own tastes? Yes, it's Trek and yes it is within an established format or genre conventions but not so much because that's what the target audience expects but because that's what the writer is most interested in.
This is certainly is true for me but obviously I can't speak for everyone. Some writers may pander more to their audience than others.
I've noticed on fanfiction.net that some writers ask for suggestions on where to take the next chapter. If somebody requests a particular character, or the resolution to a situation, for example, that's what the author promises to write.
Seems a bit lazy to me, as though the author has no idea where the story is going, or how it's going to end.
I think writers also do (or probably should) write to the audience at least a bit, in the sense of creating art that is accessible and understandable. I don't believe it's pandering to make the vision clear. After all, the readers aren't in our heads (at least, I hope not). Hence if the character's internal motivations are important, they need to be explained or at least hinted at, and not just - oh, the readership will get it.
Well, what happens if they don't?
That's what feedback is for.
Or if the reader simply doesn't want to spend the effort to figure out a poorly-written story and moves on to something else, that's a valid response, too.