User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-86.180.53.240-20171010132719/@comment-29963364-20171010165649

@ A FANDOM user

Samael was sealed because his mere presence is harmful to all beings, not just dragons (although, dragons are hurt more by it).

It was agreed by the Factions of the world (or just the Three Factions) that Samael would be sealed away. That's why it was such a big deal that Hades unsealed Samael and gave it to the Hero Faction in the first place. He was breaking treaty made by the major Religious/Mythological Factions.