Eggs, in fact, are relics from the Ancient Era.
The so-called relics from the Ancient Era were not hatched from eggs, but rather they were descendants of the supreme bloodlines from the Ancient Era. As the end of the Ancient Era approached and the catastrophe that would end the world loomed, the mighty ones sealed the bloodlines of their descendants in primeval coffins to prevent their demise during the catastrophe.
After the catastrophe, all the existing primeval coffins were referred to as relics from the Ancient Era. Although they were descendants of supreme bloodlines, they were somewhat affected by the catastrophe. Their bloodlines were no longer pure, and their innate talents had somewhat altered.