Nah. What ruined it was the fan response to the ending.
That for aure was the ending he had intended for the books and provided to D&D with his outline of major plots points… There’s no way they made that up on their own. The dramatically negative response to the ending means he would have to redevelop the entire ending again.
Most people didn’t really hate the HBO ending that much after reflecting on it. What we hated was how God damn rushed and sloppily it was done. We were also furious how poorly the Battle for Winterfell was done. If they’d done the proper arc for Daenerys descending into madness, more of Bran being positioned for taking the throne, etc etc, it wouldn’t have fallen nearly as flat. Instead, the show skipped all of that development and so all the character choices felt completely random and stupid.
Anyway, I agree with you that that’s why he’s lost motivation for it. Iirc, he initially supported D&D and said that was the intended ending. It wasn’t until later that he backtracked and said that it wasn’t. But, yeah, we’re never going to get the last books.
The poor ending was entirely due to the hubris of Dumb and Dumber who were greedily looking ahead to their next projects. HBO was willing to give them as many seasons as they wanted after season 6 and they said, "Nah, we can do it in two seasons. And instead of ten episodes each they’ll have 7 and 6 episodes because “Fuck You”. They could have handed it off to someone passionate if they were bored, but again, hubris.
Eh, there were a lot of decisions that essentially made it impossible to write a good story for the ending. Just off the top of my head:
- Arya using her Faceless Men training once. She could have probably just paid to kill Walder Frey…
- Zero payoff to the big Targaryan reveal - other than it pissing off Dany
- Why Arya decided to go travelling.
- Bran barely used his abilities. Man could’ve warged into several beasts and fought during the main battle, and outside of being a moody bitch he doesn’t really do anything other than act as bait.
- Who was the legendary lord of light? Was it Jon? It kinda seemed like it, but it makes a lot more sense for Arya to be the one.
- Thematically, it would have made a lot more sense for Jaime to reject Cersei, and for this to be the catalyst for her to go crazy - with Dany going crazy from achieving slow victory that chipped away at her claim.
- Varys was too clever for his story to end like it did. IMO he should have been able to escape his capture, and fled away from Westeros.
Unpopular opinion: The show runners did the best job they could, because with the limited time they had there wasn’t really an option for a better ending. They really needed at least another two seasons, but the reason GRRM hasn’t written another book is because he knows he’s written himself into a corner - and rather than try to fix it through TV and give himself an “out” he criticised the ending he probably had a hand in creating, and won’t ever finish the story.