When it comes to sci-fic, I dont think a book can do it justice in the same way a movie can. Since with sci-fic, in most cases, you are in a fictional world that you cant relate to. Describing the gadgets and environment in a book may leave the reader clueless as to whats being talked about. Foe example, I dont think I would enjoy The Matrix in book form
Hollywood make plot and scenarious for all their movies and with correct motives to create something fascinating anyway or to create another american hero who will alone (or with little help) will save the world/country from bad guys/robots/infection/other nations and so on.