GOT happened because the author was okay with putting up with the mess Hollywood makes of a book (or series) in exchange for money... It's a hassle, but the money is good.
George RR Martin waned to write for television and movies BEFORE he was a novelist. Also: I hate people like the one in this comic panel above. "I had the idea to translate someone else's successful idea first..." These are the self centered and willfully ignorant.