I'm very frustrated with the Christian fiction market, both children's and adult. Aside from the "following the trend" problem, just the basic philosophy many of the Christian publishers have strikes me as odd.
First, some require there to be an element of evangelism to take place in their books. Not that I'm opposed to that. But the problem is, the Christian publishers will only sell their books in the Christian bookstores, or in sections in mainstream bookstores that only Christians are looking at to begin with. As such, what point is there in the evangelism angle? They are evangelizing those who are already Christians! Preaching to the choir, as it were. Which makes the whole evangelism requirement rather pointless.
Second, Christian publishers tend not to want gritty or raw topics handled, forgetting that this is a pained, sinful world where people make mistakes. And while people CAN make mistakes in the Christian books, they are only allowed to make "approved" mistakes. Nothing too terrible, unless it is an unrepentant character OR is a character who ultimately becomes the object of evangelism. But, what about the average Christian out there who ALSO makes mistakes? The same "masks" that people wear at church must be worn in books, because, heaven forbid, we might actually have a character/church member who, for example, swears. Or how about the Christian (character) who has doubts? Many publishers just won't allow that.
Third, a great majority of Christian fiction I've read is, quite frankly, second-rate. It is predictable and unimaginative.
If a Christian writer wants to influence the world, I think they should be targeting the SECULAR market. Write a book that a secular readership wants to read that, in some fashion, reflects the gospel message...even if only in a subtle way.