Because whether Martin or the production staff of “Game of Thrones” would admit it or not in public, the TV series is generally based on the novel, amid some variations every now and then.
In a recent interview, Martin revealed that the sixth book of his fantasy novel series will have a great twist happening on one major character. He said that the great twist on “The Winds of Winter” is going to drive readers crazy but later on said that he is still thinking whether to go towards that direction or not.
George Martin also detailed in the interview that the writing progress for “The Winds of Winter” was quite hasty at the onset.
Because of his prior commitments, he actually had to stop writing for a while. He disclosed that he was red hot on writing the book, but he had to put it aside for six months. Martin said that he should have just continued from there because he was so into it and everything was moving fast for him.
So when he switched gears, he lost the momentum. He had to anyway as he also had to focus on the editing phase and the subsequent book tour. But he was still confident then that he can get his writing groove back because, as a veteran writer, he says that the iron does not cool off for him.