David Rothkopf has a good article on this
North Korea is dangerously close to crossing a line. Not the line that leads to a missile attack on the United States, but the one that separates being a rogue state from being a parody of a rogue state. Pyongyang's bluster is as comical as its nuclear threats are implausible.
It is by no means assured that Kim Jong Un has fully consolidated his authority. By ramping up rhetoric, but exercising restraint with respect to actual military actions, the regime can count on the fact that the United States and South Korea are not going to take the first step either.
The result is that North Korea's exercises and threats of retaliation have been successful in deterring attack, even though none was coming.