I had another thought about this... What if Asterion's suffering is a battery of sorts. Someone who lived in the times of the Olympian gods and goddesses and by continuing to exist keeps them in power. We learned from the story that gods without worshippers lose their power and eventually fade... By keeping Asterion alive in the labyrinth they have a captive power source for the rest of time, plus it's inspired all the myths that we would recognize today about the Cretans the Romans and Greeks. By keeping the old gods somewhat active in popular culture and myth, and strengthening the existing mythos, they gave themselves another possible way to stay alive...?