The book market for young readers can change like lightning.
For a while they wanted vampires and zombies. Now it's mermaids, or is it something else already? Fantasy was all the rage, but now is science fiction on the rise? I've heard you can't sell plain old historical fiction these days, but it used to be a major staple.
The biggest problem with this is, books grow slow. If I start today to write a book that fits the latest trend, by the time it's ready to sell, the latest trend is over.
So how do I find the courage to move forward with a project, knowing full well that by the time it is done, the genre may be out of style?
I have to forget all of that and focus on writing the best book I can. And then if I can't sell that book, I move on and write another one. Someday, somehow, everything will come into alignment.
The world needs great stories of all kinds. Write what you love, and have faith that there will be a place for it.