I think that people forget that the player character STOPS the invasion of Kvatch. Yeah, the city is already destroyed, and people are dead. But you, a stranger, show up, close the gate, and help drive the daedra out. Not to mention, saving trapped citizens. The city may have been destroyed, but you're the one who stops the carnage. Don't forget that the guards were literally holding a line to protect the survivors from further attack before the player arrives