You're way off with this.
First, what makes a great author is entirely subjective. Second, even if an author writes a great book, it may not translate well into a movie. Even if you break a book up into multiple movies, you're probably going to have to leave a lot out. There's also the inability to effectively project the thoughts of characters in a movie as you can in a book. It sounds to me more that you think the authors YOU like should be made into movies.
One last thing is that not all the movies made based on King books have been bad. In fact, a few have been excellent. The real problem is that his horror hasn't translated well to movies. Stand By Me, The Green Mile, and most definitely The Shawshank Redemption were all very good movies based on King books.
Oh, and I don't know how overrated King is; he's been lambasted by many a critic. I've enjoyed reading a number of his books, which is the only standard by which I judge an author, and based on his sales apparently quite a few others have as well, so I guess he's not all THAT bad.
I believe that Stand By Me, The Green Mile, and Shawshank were all Stephen King short stories, and yes, all three of them adapted well to the "big screen". Maybe using King short stories is the secret!
A "normal" Stephen King novel is very wordy, chock full of analogies, and too "fat". King spends too much time weaving the "background" story and going out of his way to reference non-fictional locations in Maine. He should spend more time adding more "meat to the bone".
I'm presently reading Stephen King's newest book, "11/22/63", and so far, it is VERY tedious. My wife got it for me for Christmas, because of the fact that I am a JFK assassination self-proclaimed "expert".
In this very thick new book, once again, King spends way too much time referencing non-fictional locations in Maine (like anybody OUTSIDE of Maine gives a shit), and every other sentence is some sort of analogy. This book is interesting, but Kings' writing style reminds me of a high schooler trying to get an "A" in a writing class.
Obviously, the works of MANY authors are virtually unadaptable to any other media (live theatre, movies, TV).