Of course you have think their was some consideration if we say forced them into a military confrontation. Since they had at least two nukes (1994 CIA estimated four) then how many millions would died if South Korea was vaporized? We are stretched thin militarily. Japan is re-arming with at least strong naval defense capabilities under our direction. We just weren’t ready to confront them say five years ago and now they certainly have more nukes. What is scary is that the end game for China to move militarily on Asia and Taiwan is North Korea. Cut off that aid and I don’t agree with the author they will unite as a democracy, I believe Kim will attack the South.
Because U.S. won't do anything against China, economically let along militarily.
Another scenario is that N. Korea could blink, at least some element of N. Korean military. The last time N. Korea blinked is in '76 when U.S. was fully prepared to move 100km into N. Korean territory after the infamous ax murder.
They are ruthless beyond pale, but not suicidal. If combined pressure of U.S. and China(however grudgingly) it will produce results. The trouble is nobody wants to lean hard on China, and China knows it.