Steward Heir Selections.
Driven by a desire for self-preservation, it was one of the few decrees made by the council that was enforced. Heirs often fought each other to be the last person standing, but a poor stewardship left everyone involved destitute. In order to prevent the general collapse of their world order, first heirs were to be chosen in a formal rigors manner in order to manage and promote proper stewards to carry out their sacred duty to the goddess.
On paper at least, most of the time the steward heirs fought for a few generations and the one who wins inherits the title. As long as an heir existed to take the place, it wasn't required to go through this whole process. Real reasons for the selection were when the heirs were generally weak and ill-suited for the task or that the steward was threatened by their heirs prematurely.