Dude has written himself into three different corners and likely doesn’t see a (satisfying) way to wrap it up in two books, so he’s decided to give up. If the rumors are true and he gave B&B the elevator pitch version of his ending, he may be hemming hawing about how much to course correct from their version. His Bran running Westeros could certainly come into being more elegantly than the show’s, but jeez it would be very weird in its own way.