Considering what happened way in the past when Ysaarj was torn out of the planet. From what I recollect, the whole ordeal with the Well of Eternity was that they had torn a hole in Azeroth that was spewing "the blood of Azeroth." So they made the lake above it to "plug the hole" so to speak. In that sense. If Azerite is the manifestation of the blood of Azeroth, then there should already be some amount of Azerite existing on the planet. It might not be a very common material, but if it is so powerful and is arcane in nature, then it should already be a catalogued substance to mages in both factions.