The decision to shorten the final season was made by higher-ups at HBO, not by the creators. HBO doesn't care whether or not people are happy with the way things ended, and with the obscene amount of money that they dropped on the series, they weren't about to incur further losses by taking on more staff. The special effects, the set designs, the costumes, not to mention what they spent on paying the cast and crew and shuttling everyone all over the place, those things ate up a tremendous amount of money. The people at HBO decided that it was time to end it and the creators were told they had 6 episodes to conclude things. Did they bungle things terribly? Yes. Will the finale go down in history as being one of the most disappointing endings in television history? Absolutely. But they were working from Martin's instructions. It could have been done much better, but apparently the ending we got was the intended one. That's just as disappointing as the shite execution really.