Does the Cycle have some purpose beyond governing the Dragaeran Empire? The Lords of Judgment seem to want to protect it (e.g. in The Paths of the Dead (book)). It is possible that the Gods derive some of their power from the turning of the Cycle, and that this turning occurs because of each of the Houses acting according to their natures when they are in control of the Empire. For example, Zerika, as a Reborn Phoenix, is bringing about the rebirth of the Empire. Perhaps when all the energy needed has been put into that endeavor, no more energy is generated for the Cycle, but the Cycle turns to the Dragon, and then it becomes Norathar's responsibility to act as dictated by the characteristics of her House to continue to cause the Cycle to turn.