Lynn Price at Behler Blog explains why even a good book can have trouble getting a publisher.
The part on market trends is important. The time delay between submitting a manuscript and getting it on the bookstore shelves — often measured in years — make it almost certain that the bandwagon you’re trying to jump on won’t be moving by the time you’ve gotten on board. It’s a lot like the stock market in some ways.
So you don’t really lose out on market opportunities by writing what you want to write, and what you’re best at writing. Who knows? Many of the hot trends got started by authors who struck out on new paths. Maybe you’ll be one of them.