Sentinals have wiped them out and destroyed every trace of old civilisation.
Then again, it’s just an excuse; having them does not solve the issue. Most devs these days will prefer procedural generation with handcrafted POI on top, but having the player spend time on them is the issue, because HG are terrible at creating POIs with lore.
Let’s hope that he is doing open-world exploration right this time, instead of implementing a bunch of disjointed mechanics without a purpose to artificially lengthen the life of the game as a “sandbox”.