I remember reading about the Narnia movies and so just looked it up on wikipedia to refresh my memory; the films underwent production issues (Disney didn't want to do the third one) and having to get replacements, budget issues, and the CS Lewis Estate having disagreements with said companies. That said, the fourth, The Silver Chair, is slated to be next and should be filming soon.
I think one "rush" to get the first three movies out is that the actors for Peter, Edmund, Susan, and Lucy needed to be around the same age for all of them. Even though they appear in later books (Horse and his Boy and Last Battle), they could get away with being older. I think they're doing the Silver Chair now because they need the actor playing Eustace to seem the same (assuming they'll still use him).
One "weird" thing about Avengers/Capt America is that the actor was the same one who played Johnny Storm in the FF films. If they ever revisit those films, I'm guessing he will have to be re-cast...