To protect the residents of heaven from the chaos hell brought, to keep their population controlled, and the chances of being overrun...Especially Emily. It was why she kept the dear little seraphim from the truth of the yearly extermination. Though, she'd chosen to accept hearing Charlie, the princess of hell's, case about her hotel being used to redeem the sinners cast down there. She knew learning would lead to Emily questioning would lead to her becoming a fallen angel, and it worried her.