I long assumed that - given the Garleans were introduced has having a unique physiology (third eye) and a unique limitation (near-total inability to manipulate aether) - the cause would explored much earlier than this (even if the reasoning was explicitly stated as, "fluke of nature, don't worry about it").

Given the fact that it only even manifests among "pure blooded" Garleans, the only theory I ever had before giving up on needing one at all was, "Allag did it", lol. Some kind of artificial control on a mage-heavy population.

Maybe they held off exploring it until the Garlean expansion and then, whoops, we skipped that one and went straight to Endwalker.