This was my first thought when I saw this, if it was so important to record, and you have the ability to produce such accurate monuments, why not write the warning down?

Thinking about it though, they probably did! Imagine, it would be a written story, on tablets, as well as word of mouth, given the difficulty of writing and carrying tablets its likely as population spread out to be carried on via word of mouth ("classes" as you
say), so its been a 12000 year long game of "broken telephone".

[** note below I am illustrating points, I am not claiming these are true facts, and "you" means people in general not specific attack on OP]

Besides, even if they did, would you believe it?

If we look at the world right now, there are numerous written histories, in tablet, parchment and modern form, and how many do people believe?

Lets take one of the most common, the Bible, now here is a written history that says if you check out your neighbours wife then die before repenting to Jesus your not-so-loving Father will burn and torment you forever.

Now, how many believe this? Even with this "recent" story, many have different interpretations, many don't believe, etc, and yet its part of our written history.

Sumerian tablets telling of (aliens?) like Enki and Enlil coming here, creating us, just generally messing whole place up, etc etc, how many believe it, how many say "bs" ?

So imagine what would happen to a 12000 year old story about a magical ray of light coming from the heavens to destroy everything? After time, how many would believe it, how would it have changed over time?

Besides, do we not still have record of this coming event in some forms? Does the above mentioned Bible not contain a prophecy of a day when the earth will shake and tear its apart and fire from the heavens will wipe us out? Of course its been amended, and all those years ago the story was changed into a form in which this will be done by a psychopathic god to punish people for various random wrong doings, and the only way to escape the catastrophe was, in essence, to pay money to the church (which is what it ultimately amounted to), so here we have the human issue, those in the know manipulating important history for their own gain.

Then look at how much history has been lost, either accidentally, just by petty destruction from pointless conquests by Spanish, English, etc to dominate and crush natives, or by deliberate attempt to hide this history. Afaik, one of the first locations taken in one of the Gulf wars by US was a temple of some kind packed with old tablets, plus the raiding and removal of artifacts from museums. Makes you wonder if they were looking for or trying to destroy something.


“And some things that should not have been forgotten were lost. History became legend. Legend became myth. And for two and a half thousand years, the ring passed out of all knowledge.”

― Galadriel in The Lord of the Rings: The Fellowship of the Ring, The Lord of the Rings