He could say tomorrow that he has no idea how to end the story, that having become rich and famous he doesn't have the same connection with the grit and grime that made the story work, and he wants to focus on writing breezier, more fun faire instead. I'd be fine with that. He could also say that seeing the story beats he planned play out in the show broke his confidence, and he doesn't want to move forward until he has a different idea he's comfortable with; "I don't know if I'll be able to finish" is a valid answer.
These continual claims to have pushed out endless chapters are just tiring, though. The book would have to be hundreds of thousands of pages long to contain all the progress he's claimed to have made on it, at this point.
What if he does know how to end it, and that isn't the issue?
What if he has the same connection to the story as ever (after all, he's written hundreds of pages of material for Fire & Blood, and TWOIAF), and that isn't the issue?
He's on record as saying writing has gotten harder as he's gotten more elderly. He's on record explaining his (terrible) writing process. He's on record explaining his list of commitments and hobbies that, whether fans like it or not, have always extended beyond 'writing ASOIAF 24/7.'
What if his long-running explanations of what characters he's writing in TWOW at any given time over the last 10 years have all been entirely true -- he's just had to overhaul things again and again because he's a perfectionist, and the world is so stupidly intricate that these rewrites are mega time-consuming? (There is of course the popular speculation that he had a near-complete TWOW in 2015-2016, but wasn't satisfied with it for whatever reason, and scrapped a lot of it.)
What if the reaction to the show's ending didn't faze him that much, because (1) he envisions his being fairly different overall, save for a few major tidbits he gave D&D, all of which we know, and (2) he was just as disillusioned with the show and its leadership, but obviously can't say anything because of his relationship with HBO (we already know he and D&D had a falling out well before the show ended)?
Pretty sure he's said he wrote twice as many manuscript pages for ADWD over the entire process than were in the final product, and the final product was already gargantuan. TWOW is, one imagines, probably even bigger than that, with even more trial-and-error.
Overall, I don't doubt that he's being honest. And while he keeps his cards close to his chest about the specific causes of his struggle (because why would he spoil people?), I don't interpret that as him cagily procrastinating writing. I believe he writes quite a lot; his process just sucks, he's old, and the story is an unwieldy behemoth. What I'll never understand are the people who want him to prostrate himself and proclaim he'll never finish before he dies -- talk about morbid. Or those who want him to 'admit he's given up' when it's abundantly clear he hasn't.
If you're tired by his progress updates... stop paying attention to them? It'll be out when it's out regardless. He's not making press releases stringing people along; he's posting diary entries on his personal blog, complete with mood emojis.
