User blog comment:Wachotenefaso/Why don't Winchester ask angels about the Mother of All?/@comment-3481504-20120428021817

Well, a war, yeah. But not really the apocalypse. Anyways, I'm not sure, possibly because she's older than them.

And you're right, they (Dean, Sam, Bobby, etc) never directly asked who she is, or what she wants, but Cas did help them with the case, hence "Mommy Dearest".