That also begs the question, why the hell was Azmo besieging that place anyway? and what was he doing in the Arreat crater? It couldn't have been to find the Black SS as the siege was already well under way before leah and the player arrive.
I recognize that this is a video game and as such, one shouldn't expect a Homeric epic, but such blatant plot holes are indicative of plain laziness on the part of Blizz. It's really just embarrassing to watch...painful even.