A big theory going about is this:
Nyx: The Creator of all
Wyrd: The Preserver of all
Leveller: Destroyer of all
So this could explain the cycle. Nyx creates something, Wyrd preserves it and makes it interesting (like weaving mans destiny) and the Leveller destroys it a thousand years later. I think this is based on some Hindu god thing or somat, I can't remember. I like the sound of it anyway!