It also needs to be said, and I say this as a fan, the first book is pretty dull. Doing a direct adaptation of that story specifically would be incredibly difficult to do in a way that's going to keep the attention of a mass movie audience, and ultimately, a movie that's going to be as big as The Dark Tower would need to be overall, would need to capture that audience. That first book needs to be part of the story, but really it only exists to set up what comes after.