It's a shame that the Narnia franchise gradually fizzled out after Dawn Treader, it could have been another great one to follow in the footsteps of Star Wars, Middle-Earth and Harry Potter, especially with the battle scenes of the first two being so much like Middle-Earth in scope thanks to Weta being in charge of the effects. However a key flaw as pointed out in a recent video on its downfall was that because so much more time passed between each book than with Harry Potter, for instance, and because the Narnia stories were meant to be individual stand-alone tales, by and large, rather than part of an overarching story arc, it meant the main characters would have changed too regularly in the film series if they had continued it, making it jarring to watch old characters continually vanish and be replaced with new ones. Of course the only way to change that would be to change the stories irrevocably to somehow keep the main four original characters going through the entire set of nine stories, which would have been disrespectful to the later stories and I'm glad Disney didn't do.