It was never intended for film or TV. It was almost intentionally unfilmable.
“I had worked in Hollywood myself for about 10 years, from the late ’80s to the ’90s. I’d been on the staff of The Twilight Zone and Beauty and the Beast. All of my first drafts tended to be too big or too expensive. I always hated the process of having to cut.” When he took up novel-writing afterward, he recalls: “I said, ‘I’m sick of this, I’m going to write something that’s as big as I want it to be, and it’s going to have a cast of characters that go into the thousands, and I’m going to have huge castles, and battles, and dragons.”
https://ew.com/article/2011/04/04/game-of-thrones-hbo-george...