I've actually done a pretty good job explaining to people why I became disillusioned with fiction as literature, preferring auto-biography (and weblogging!). And now I don't need to write it down, because Nowheresville has done it for me:

I thought about what I don't like about Christian fiction, generally, and it is this. We can't put words in God's mouth. We cannot pretend to know the mind of God. We are lying if we say we can know why he decided Aunt Jen would have faith in him but Uncle Ted would think Aunt Jen was nuts. And this is what most Christian fiction writers are doing. They are pretending to be God in that they determine the actions of God.

Fiction is false; God is the only author of reality.