User blog comment:Chaos11394/Any Ideas for new villians for future seasons!/@comment-69.255.188.213-20130101043245/@comment-3481504-20130103000710

So....why make it a Monster of the Week or a primary antagonist (Big Bad), when Cas could easily kill it? It might work in a episode in a scenario where Cas is busy or preoccupied and can't help.