Movies are limited to what they can recreate. Granted thos limitations have eased with the onslaught of CGI/digital technology, but still have limitations.
Books are only limited by the authors ability to relay his vision in words. The greatest authros don't have any trouble with this. They can do things that could never be done in a movie: whether it be Fleming describing 007's favorite breakfast, the exquisite detail that Tolkien put into describing the lands of Middle-earth, Dickens presentation of the time the story is set in (best run-on sentence in histroy!) or Victor Hugo's relaying Jean ValJean's thoughts and feelings as he suddenly has a revelation of his own crimes and desires nothing more than to return the coin to the child from whom he stole it.
Books spark the imagination to fill in the gaps as well. When yo look at a movie screen, if it isn't on it, you won't imagine it being there. But when you read a book, you develop your own image of the characters, places, items, and what happens - not some directors vision which may not even correspond with what the original author intended.
For instance, I tried watching David Tennant's Hamlet and it just didn't work for me. Shakespeare's original play is brilliant and Kenneth Branagh is, AFAIC, the penultimate, if not the ultimate, portrayer of the Prince as well as being in the same position as director of several of the Bard's greatest stories. But I still have an image in my mind of Prince Hamlet and Elsinore that has yet to be seen on screen. the same with 007 and Sherlock Holmes and Ebeneezer Scrooge. Despite the great actors and performances over the years, when I read a 007 novel or a Sherlock Holmes story or A Christmas Carol, I don't picture any of the actors who have played Bond, or Jeremy Brett, or Alastair Sims/George C. Scott/Patrick Stewart. I have an image in my mind of the character the way I was first introduced to him or her: as an image presented to me in writing and molded over the course of the story or even many books.