Freedom of youth
Here each generation is long lived.
They have sufficient time to develop languages, agriculture, civilisation; to invent religions and sciences; to reflect on their condition through art. When they reach maturity, they lay eggs deep within the planet in caverns warmed by nuclear heat.
While the eggs gestate, their parents-in-waiting return to the surface where they dismantle everything: raze the cities, pulp the books – until no work of their hands is left. Once they die, the eggs hatch to a world that appears untouched.
Why go to all this trouble? Because they want their children to have what they had.