The only other people that have been around The Wound were either the Earthen Ring, a few members of the Cenarion Circle (including Hamuul Runetotem), Magni, and a bunch of goblin Azerite tycoons trying to expedite this stuff like oil.
And the only people that ever actually went into the Chamber of Heart itself was Magni, the player, and the Aspects... while Anduin was busy with a war and Thrall was basically retired on Outland until Saurfang had to drag him back because of how bad things gotten.
(There's also this one bit of nugget of info that everyone doesn't know about (or they did and forgot)
The Chamber of Heart was created by Archaedas. Knowledge of its existence was heavily restricted to protect the world-soul; it was unknown even to Highkeeper Ra, who apparently did not have the sigma-level clearance required. Source. )
Not to mention that most people didn't treat Azerite like it was the life blood of Azeroth but has a new form of resource that works as a miracle tonic and volatile substance that is more potent than gunpowder.
So literally every character except for Magni, the player, and the Aspects didn't know this whole time that Azeroth is a living planet that can talk. And even though Magni claims to speak for Azeroth, NOT ONCE... NOT EVEN ONCE DID HE TRY TO STOP PEOPLE FROM USING AZERITE IN THE WAR! (Then again, even if he did it wouldn't matter much because one side would've taken more Azerite and turn it into an arms race thanks to Gallywix and the Venture Co. trying to profiteer from it.)
Bottom line: We (the player) are ten steps ahead of everyone else in the story and now we have to get them up to speed. And the Azerite plot with Magni isn't the A plot... it's the D plot of the story. The A plot being the War, B plot being N'zoth's awakening, and C plot being Mechagon.