HBO gave them that option, yes. Also this season could've been split into 10 episodes but they decided to do 6 longer ones instead. However the fact of the matter is, they're out of material. These lads are great at bringing books to life or whatever you call it but they're mediocre at best when it comes to writing shit themselves. People have been torching them non-stop for this season, imagine dragging it out for another 2 they'd be hated worse than the lovechild of Joffrey and Ramsay combined.