As others have said, it has less to do with CGI than with the fact that some novels are very much based on a character's internal world, and you can't always show that on film. Like, a character spending 50 percent of a book pondering the meaning of life is hard to film.

And even if you could, it might be boring (while the book might be brilliant) or so far removed from the book you ca't really call it an adaptation anymore.