The overwhelming power of Michael's Untamed Awakened, combined with the support of the Untamed Army, was enough to defeat Olivia Blaze and her subordinates.
Once Olivia died, the Awakened tried fleeing. They scattered in all directions, hoping to survive, but Michael and his subjects didn't let them. Leaving behind a single Awakened in the Sacred Desert could end badly. The survivors could recover, grow stronger, and attack Michael's people as he expanded throughout the Sacred Desert.
The chance was present, enough reason to slay the Awakened to remove any possibility of retaliation.
Conquering the settlement had been fairly simple, but the innocent citizens posed a problem. Michael was unsure what to do with them. He could slaughter them for their energy influx and the loot their corpses would produce, but killing the innocent after the battle ended didn't mate him better than the Blaze Patriarch and his family members.