Narnia Out of Order

Now why would Disney go and make the Narnia movies out of order?

I understand why the film makers wouldn't want to start with The Magician's Nephew, which is the first book according to the storyline. C.S. Lewis, after all, didn't write the book until after The Lion, the Witch, and the Wardrobe. I suppose I can even understand why the makers would hold off on the book even as they move on with the series: The whole thing reads a bit like the first few chapters of a long book.

But why skip The Horse and His Boy? Is it the Arabian flavor of the backwards Calormenes? More practical considerations could be holding the day, of course, such as the need to make all of the movies in which the Pevensie children play central roles so that the actors don't out pace their characters too dramatically in aging, as with the Harry Potter movies (which has been a huge distraction, for me as a viewer, anyway).