I'll give you an easy answer for this question.
MOST PEOPLE ONLY CARE ABOUT WHAT THEY WANT/THEMSELVES.
Though by no mean is EVERYONE like this, sadly, more than half of people are. I've had a jerk like that too, though slightly different.
I recieved a request from someone to write a male/male pairing with a certain fetish. There was no time limit, and it was requested as a oneshot. There were NO other specifications.
So I agreed, wrote their story, with the pairing and fetish they asked for. A slightly longish oneshot, but nothing complainable.
Not two hours after posting it I recieve an emial from the person who requested the story.
They FLAMED me.
Seven and a half paragraphs of 'What the hell kind of story is this?' and 'Where's (a completely different character), I said use them too!'.
Completely confused, I sent back 'You never asked for that character. You said two people, not a threesome.
They then went into another almost story-length rant about how the story sucked and that I wasn't putting my full effort into it. Also that they had 'specifically asked' for the third character and that I was just a 'lazy-ass who didn't want to bother answering a simple request'.
It made me so angry I deleted the story and blocked them from emailing me. After that, I got a few flames on some of my other related stories, and I'm quite sure they were theirs. The typing style and wording were the same.
So don't feel alone... there are idiots everywhere. But there are also good friends.