Kim Jong-il and Jong-eun both see signs of their regime wavering, and the bomb is the way out of this. They believe that "The bomb" is the way out of their current problem. Whether outsiders agree with it or not is beside the point.
With world financial market on the thin ice, they can now get more focused world's attention, and loud call for appeasement from banksters.
Financial Times, beat your appeasement drum again. You did when Cheonan was sunk. Please don't fail us and do it again./sarc