Visible history is generally written by the beaurocratic/violent society, not their egalitarian neighbour. If you think further back in history, I'm sure you'll recall "the great periods" as we call them, marred with obvious artifacts from oppressive societies.

Their egalitarian neighbours where only just starting to discover. In part because their traces are less obvious, and in part because we've had a mental confirmation bias against finding them. I refer back to The Dawn of Everything if you want more details!