I was going to start this next paragraph thusly: "The main reason picture book manuscripts are so difficult to sell to publishers is..." and then tell you the number one reason. But no, there are several reasons and they all carry equal weight. So let's just look them all (or some, at least).
1) Probably close to eighty-five per cent of the submissions we receive in the children's division of Fitzhenry and Whiteside are for picture book texts. Why? Well, I can't be sure, but I have a hunch that it's because many new authors who do not yet feel ready to tackle writing a whole novel assume that writing a picture book will be easier. After all, picture books are short, the language in them is simple, and they're fun. The images in the book can tell parts of the story or at the very least enhance the words, meaning the writer can be a bit vague---remain on the surface. Kids are easy to please, it's the parents you need to impress since they will be the ones forking out the dough to buy the book, so if you can get a lesson in there somehow that parents will appreciate, writing a picture book should be simple. That's the assumption. But guess what...
That assumption is dead wrong. Picture book text is exceedingly difficult to write, and kids tend to hate blatant lessons.
4) And then there're rhyming manuscript texts written by people who don't understand poetry. Let it be said that if the prose for a picture book text is hard to write, rhyming picture book text is triple that in the difficulty department. All it takes is one awkwardly worded phrase to confuse a child and therefore ruin the story. And if your editor tries to clarify the sentence (which kindof is an editor's job), that can throw the whole thing off---rhythm, meter, beat... If you want to try a picture book text that rhymes, you need to first study poetry. Do not underestimate the power of a messed up rhyme scheme and the cleverness of a child that will definitely pick up on it when they hear it.
5) Picture books are very, very expensive to produce. Many of them are hardcover, most of them are full colour. This requires not only the expense involved with printing 16 full colour spreads on the specialty paper needed for colour (most picture books are 32 pages long and all of those pages must be of a certain type and quality), but the artwork must be stellar too. That means there will be an artist involved unless you are one of the rare creatures capable of both killer wordsmithing as well as visual art producing (a very rare animal indeed). As you can imagine, none of these things are cheap. If there is any concern that the book won't sell, the costs involved with producing it won't be in the cards.
And there you have it. We get heaps and heaps (and heaps and heaps) of new manuscripts from authors who want to publish in a genre that has the lowest demand for new manuscripts. This means your manuscript must be absolutely knock-me-down amazeballs. Picture books are a buyers market, which rather puts off publishers from picking them up.
I'm not saying this to discourage anyone. There are some wonderful new picture books out there (Jon Klassen's This is Not My Hat, Drew Daywalt's The Day the Crayons Quit, B. J. Novack's The Book With No Pictures and others are all fantastic, unique books) and more will come. But before you begin purchasing postage to send out your picture book submission packages, take a tour of your local bookstore, library, and your child's bookshelf to see what is already available. Chances are, those books are not going anywhere anytime soon.