Endwalker's message (spoilers!)

[KizuyaKatogami]

I think a lot of it came down to Venat not wanting to create a time paradox of some kind. In her eyes, the time of the Ancients was coming to a close. Even if she had come forward with the information she had available, her peers might have thought their civilization too big to fail and ignored her. That and Meteion was hanging out at the edge of the known universe, where she couldn't be reached (well, back then anyway). And the Final Days hit them pretty soon after she vanished, so they didn't have time to construct a means to reach her. Venat was looking to preserve a future that could still be saved.

The thing is, even though Emet believes us, he says himself he needs to assist us due to his duty for the star, in the odd chance we are telling the truth. Him and Hythlo also both remark they know they were mind wiped, they can feel it. It’s as simple as her saying yes you were mind wiped. This is why. x,x, and x is happening etc.

It's also possible that Zodiark would have lead to the extinction of the ancients given that more of them were basically feeding themselves to it in hopes it would return the world to how it was before the end of days. They basically stopped looking to the future and wished to return to the past. Which by retaining the knowledge of Meteion's reports was a mindset that lead to the end of other worlds. So even if Zodiark had successfully restored the world to how it was before the end of days, the mindset created by the event would have likely lead to an end similar to other worlds meteion visited had experienced. Also given emet selch's initial reaction when the WoL informed them of the end of days it was likely reasoned providing that info after the memory wipe when no physical evidence was available wouldn't have accomplished anything.

I dont really agree with this. People act like they were sacrificing people every other day lmao. They had only sacrificed people a total of two times. A 3rd was on its way however it should be noted based on Emer's short story, they were extremely split on the decision. It's unlikely after the 3rd set they would continue to sacrifice to him, at that point what would they even be sacrificing for? They'd have everything back.