Anyway, companies should hire people who are both passionate about the source material, and want to make something cool and new in that world - not robots who are just going to recreate the original work beat for beat. If I wanted that, why wouldn't I myself just, you know, read the book?

While I agree in general, different mediums have different strengths and weaknesses, and different appeals. For example, a book is great at telling intricate stories, but will generally fall flat when trying to create an exciting spectacle. Even if the story is very similar, these different strengths (esspecially, but not exclusively when the material is tweaked to account for it). The Lord of the Rings movies come to mind as a good example of that. The books create a cohesive world with intrecate details everywhere whereas the movies, feature so many stunning scenes that you just can't do justice with words alone at the cost of many of these details. You can cover the same story without major core changes while providing a very different and still worth-while experience.