I'm not happy with what D&D did, but GRRM deserves at least 75% of the blame for this. D&D are likely angry at him and feel that he hung them out to dry. The truth is that he did, and I'd be pissed as well if I were them.
When this whole series was being discussed and greenlighted, D&D -- and later the actors -- signed on for seven seasons, one for each book in the projected series. They did that based on the belief that would be plenty of time to tell this story the right way, and that belief was based on in-depth conversations D&D had with GRRM. The only guy who could possibly have known that it would take more than seven seasons -- GRRM -- was fine with that plan. So everyone went into it with the expectation -- memorialized by contract -- that they were signing up for no more than seven seasons. Those initial discussions all happened in 2006-07, and HBO formally bought it in 2008.
D&D also were told, by GRRM, that they'd be adapting his novels for each season, so they'd have all that source material and wouldn't be writing from scratch. He'd also write at least one episode per season. The projection that they'd be responsible for writing an adaptation directly impacted their projected workload, and the creative demands on them to complete this massive and complex story in a satisfactory manner. The most recent novel then published was 2005's A Feast For Crows, and they were assured by GRRM that he'd finish the series in time.
GRRM is an incredible writer, and the story he created is amazingly complex. The only person truly capable of finishing that story and keeping it the same high quality was him. D&D were not able to do that, and they knew it, which is why they were adapting his story rather than writing their own original one in the first place. The funny thing is that GRRM said he'd never pull a Robert Jordan, and have someone else finish his story if he couldn't. Well...guess what?
We all know what happened -- or rather, what didn't happen. Since the publication of A Feast For Crows in 2005, and through the entirety of the development, shooting, and broadcasting of the series, GRRM completed exactly one of the three books remaining to be written. One book in 14 years. And GRRM hasn't even finished one book -- not one -- since the series premiered in 2011 (he turned in the manuscript for ADWD before the first episode of the show premiered). So, the roadmap D&D were promised by GRRM to finish the show in seven seasons ended long before the finish, and the story GRRM had agreed could be told well in 7 season ballooned well beyond that. D&D were now expected to take over the creative process entirely, writing a series whose complexity and literary quality were beyond their (or anyone else other than GRRM's) capabilities.
So now, GRRM is out there saying that he's "sad" at the way the series is enging, and it really should have gone 11, 12, or 13 seasons to be told the right way. Seriously?? I can pretty much hear D&D saying "if that fat fuck had told us at the outset that we needed that much time to tell the story the "right way", we wouldn't have signed on, we couldn't have gotten that big a commitment from the actors either, and HBO would never have agreed." And they'd be right. I recall there being issues years ago with the actors' contracts when they were trying to go beyond seven seasons because the actors weren't signed to it. The idea that it should go to 10 seasons or something...D&D didn't sign up for that, and neither did the actors.
So yeah, D&D have been little bitches and done a crappy job since the books ran out. But in their defense, they were never supposed to be in this position in the first place, and the only reason they're in this position is because GRRM failed to come through on his commitments to them, and because he screwed up in his representation that the series could be done properly in just 7 seasons.
