Most people probably didn't think Blizzard would be so retarded as to waste N'Zoth and Azshara in a faction war expansion.
These people here in this thread are masters at hindsight, but back when BfA was the current expansion, a lot of people (very reasonably) didn't think Blizzard could wrap up the Fourth War (called Blood War at the time) AND Azshara/N'Zoth, all in just 3 patches.
They tried to do that, and we see that the result was a disaster. Maybe not so much with Azshara, but the N'Zoth ending cinematic has gone down in history as the most pathetic and miserable cutscene Blizzard ever made, and even calling it a cutscene is being generous.