Then why do the vast majority of the fans avoid them?
The real question is, "Why do the vast majority of people avoid books?" generally. Novels are orders of magnitude less popular than television and movies.
To hit the New York Times Bestseller list, you need to sell about 10,000 copies of a book in a week. If someone made a Star Trek movie that sold 10,000 tickets in the opening weekend, they'd never work in Hollywood again. If they made a TV episode that only had 10,000 viewers, someone would probably break their legs.
Look at the prices. A novel has an author, an editor, a cover artist, copy editor, typesetter, and various other people involved in creating it. Let's say a dozen, just for the sake of argument. A Marvel movie, for instance, has three or four thousand credited personnel working on it. Probably twice that if you throw in everyone else who doesn't rate a credit, or just gets their company credited. A movie ticket costs about the same as a book (depending on hardcover or softcover, or matinee versus super-IMAX 4D), not three hundred times as much.
You could made a movie adaptation of the ideal, perfect Star Trek novel that ended up absolutely terrible, one of the infamous failures of book-to-movie adaptaions, and more people would still unreservedly love the movie version than would ever read the book, because that's how few people read books.