There's only one easy way to say this, and it's not actually all that easy.
The Vessel were never supposed to exist. Just by asking the divine forces to create them, Ahmul's sisters had essentially broken the same rules Dahrkren had. They had been aware of that. They had also been aware that their future creations would be permitted to exist solely because they had a purpose to serve. And once they served that purpose, all bets were off. They'd go back to where they came from. The end.