Honestly the morale of their population is dropping as technology and news media from neighboring China has eroded the information stranglehold. You beat N. Korea not buy bombs but with information warfare.
This is sabre rattling, because N. Korea wants to be on 24/7 war footing to keep their population in line.
N. Korea has been in range of U.S. and allies to do major, major damage for nearly 50+ years. If N. Korea wanted to start a war, it would be highly advantageous that they started with an opening salvo to cripple S. Korea's capability of striking back.