Interesting blog post from Marissa Lingen about writing fiction vs. non-fiction. They each require different skills. Important quote:
If you haven't written a lot of fiction, you probably won't write good fiction right off the bat.
This explains why I have trouble with plotting. In non-fiction writing, either there is not supposed to be a plot, or the events are what they are as a matter of factual reality. Either way, no invention is required of the author.
It takes practice to come up with a plot that is a) coherent, b) believable, c) interesting. I'm still working on it.