"The Primordial giants were bigger than the mountains you see today. They could reach the clouds when they rose. But the generation following them was half their size. And they grew even smaller in size with time."
Ferdinand told her that there was a point when the world grew scarce and bare of resources for the living that survival of all races became questionable, especially for the weaker ones.
With their kind-hearted nature, it was then the primordial giants believed that the world which was in dire need of resources didn't need them to be around anymore. For the sake of the younger generations, they chose to sleep and let their mana and bodies provide blessings for the dying earth. It was a selfless sacrifice.
After that, the earth once again grew more than enough resources for everyone.
