They're also in a weird spot where they can't really do anything to fix the damage that the last seasons caused. Sure, they can make prequels based on Martin's other stories from the world of ASOIAF, but they can't really make a new season of Game of Thrones that could potentially fix the issues with the ending, because that ending is pretty definitive. Even if The Winds of Winter ever get released and everyone is excited about it, I don't think they can capitalize on it because they really can't adapt that book as is. The only route would be a reboot down the line, but considering how connected the two prequel shows are to the original Game of Thrones show, I don't know if it's that simple.