Because it will annoy Philip Pullman

There's a so-so review of Voyage of the Dawn Treader that has this comparison between three current fantasy series, which amused me quite a bit:

To describe the overall series comparatively, Narnia is the dorky Bible-basher at the back of the class whilst Harry Potter is the popular, apolitical kid who gets all the attention. His Dark Materials is, of course, the atheist drop-out brooding over a gun collection.