well the thing is for hunter gatherers, they simply didn't need to, and the attempt to do it would have hurt them. being hunter gatherers gave them plenty, but couldn't support static population centers like what agriculture helps provide, and the stockpiles of food that the agricultural city people had was where language came from, to keep track of it all. Hunter gatherers were just as capable as those in rich river valleys who would settle down & develop agricultural societies after the ice age, but it wasn't advantageous.

And we really could have used those notes.

Maybe they time traveled back from now and realized they don’t know how to do that either.

Never know what we might find once the glaciers retreat completely. It'd probably all be ground down beyond reasonable recognition, though.

Because most of the population is considered intelligent? Hell, every generation thinks the previous one is less intelligent than the current one. As a species we are so full of hubris as to believe we are smarter and better than we actually are. That we think we are alway correct in our assumption. You believe we didn't build back then yet there is evidence to suggest we did, only for cataclysm events to wipe it from known history. Doesn't even take much for it to happen as our currently accepted history has shown.

It's not hard to believe. They probably didn't have the right external conditions, like climate, which would need to be quite stable and warm to allow for large civilizations as a ubiquitous phenomenon.

They maybe did rarely have small rudimentary civilizations that could only prosper at trading nodes even tens of thousands of years ago, but it wasn't anything stable.

So hunter gatherers probably don't just all build civilizations anywhere on their own if enough time passes, because they first need the right conditions in order to prosper. Moving rocks requires a lot of people which would need to be fed. This requires large and stable food supplies i.e. a stable climate. If the climate changes all that collapses.

And because those civilizations were rare, they could hardly build off of another before all their knowledge was lost. It took a few hundreds of thousands of years plus the right kind of global climate for that effect to compound to the level where it is now. So, it wasn't because humans back then were inherently stupid.

If dated right, that shit scares me for several reasons.

1. Civilization and technological advances should have happened up to our level or beyond several times which implies there were several collapses, likely due to war.

2. Homo Sapiens might not have been the first or only one developing advance technology, competing cousin species living at the same time might have done as well which also begs the question, who ran the world and who were the slaves. There are myths of ancient gods that ruled the masses, it wouldn't be strange if older pre existing hominid species that had a lower population ruled over the rest that had higher fertility.

3. How bad were those wars that we can't find even the traces of the weapons used nor other clues like ancient satellites or drones, probes or spacecraft remains on the Moon at least.

4. If this has not happened and people just lived in basic hunter gatherer communities, what changed recently that we've become so desperate in forming larger and larger communities and started to invent more things. One would assume a person living 400k years ago simply didn't know as much as we do, but like, was it really that difficult to cultivate plants and raise animals instead of hunting? Why couldn't they make this simple step? It is so baffling, almost as if they were scattered, incredibly small communities that only survived in very biologically diverse regions with lots of food so nobody ever bothered to change the environment and allow only edible plants to grow. Maybe this sort of thinking was akin to magical thinking, like us now talking about colonizing space. How monstrous of a task could have been to clear out the land, keep animals out to not eat the plants or have enough food to feed animals they kept.

Lastly, why did we still discover fourth world tribes as late as the 20th century that lived in such backwards ways as these true ancient people? Was this the main cause for the effect? Lack of contact and communication, exchange of ideas and inventions that held us back? The main trigger for the change was likely the mass migrations out of Africa towards Eurasia and then the Americas and Oceania and then back from Asia towards Europe. Not only that but people out of Africa encountered totally different civilizations created by Neanderthals and other related species in Asia. Did they fight? Did they trade? Did they educate eachother? Did they intermix? Yes, this is what created our modern civilization but why couldn't people have had such migrations before? The oldest building remains we know of that are confirmed are in modern day Turkey and date back to around 10k but there are older structures in Asia that may go back more in time. Who knows how much was grinded down by the sands of the Sahara or buried deep in the soil and forgotten. It's always so fun to think about and ponder, at the very least I think we'll eventually discover much more ancient buildings in Africa under the jungle.