Yea seems that George R.R Martin, the guy who wrote the books, wasn't happy with how the show was and where it was going
“I regret to announce that the 6th season of the beloved Game of Thrones series has been cancelled. Breaking these news is not easy, I know millions of fans worldwide have been manically expecting a 6th season ever since the final episode of season 5, but I am afraid, due to various reasons, that we have discontinued the filming of season 6. The season was supposed to air this upcoming spring, but due to grieviances from the owner and purveyor of the Game of Thrones franchaise, we are simply unable to keep producing new material. I have huge respect for George R.R Martins sovereigntiy over his own world and we regret that it has come to a point where he no longer thinks that the cast and crew are custodians of his legacy. We will of course grant George’s decision to not continue filming and we will also desist the selling of merchandaise related to the TV show. I hope that all the fans will also respect George’s decision and that they will not leave the world of Westeros by continuing to buy his books. Maybe some day he will change his mind, but right now, there’s no way forward.”
said D. B. Weiss, executive producer, at the pressconference.
George R.R Martin was at the press conference too but he kept a low profile and only answered a handful of questions. This is a comment he made:
“It’s time to let this all come to rest. For the first four seasons I was very enthused by what the cast and crew were doing, but at this point I have lost all faith that the television show could ever do my books any justice. The quality has rapidly decreased and for a long time now I have felt myself not feeling comfortable with how they’re treating my story. That is why there will be no more seasons of Game of Thrones, maybe not ever. I do hope everyone will keep enjoying my books though.”
