Really? I missed that part about the West of Westerosi. When was it mentioned?
And well, you won't blame the showrunners. They wanted to end the show while the applause was at its peak, which, if you think about it is quite a feat. Most shows drag it out until viewers get tired. If I were to choose between those two options, I'd prefer this.
If I remember correctly it is mentioned in Fire and Blood.
I actually don't prefare this. I'd prefer a better script for more seasons and not jokes that will last through a generation.