Why the Emperor did not reveal himself until the time he did

[Just123456]

Yeah, the fact that he is called "the Anathema" by daemons, that his powers and faith in him just erases Chaos beings and turns the warp into plain inmaterium hints at him being something more than just a powerful psyker.

Besides all this, I find very strange that humankind leaders, scientist, and AIs at peak DAoT didn't learn anything about chaos, daemons, necron anti-warp stones and tomb worlds for all those thousands of years.

The only reasonable explanation is that something big happened, and if that is the case the Emperor, then using another name ("Neoth"?), was involved. And of course must have been a disaster. Hence the Men of Iron war, the Eldar being idiots, etc. and even more damning: By 30k all that is erased from history, censored by dogma, and the Emperor never talks about it.

Alright.