I assume that it's a "morton's fork" situation, where all options are bad.

I assume the U.S. analyzes the DPRK's military with a fine-tooth comb, and the second it detects a slight weakness, it could be game over for DPRK, which forces DPRK to continue building up it's military.

If the DPRK divests money and resources from the military to better feed and take care of it's people and develop it's own country, the U.S. will exploit that opening and attack.

If the DPRK does nothing, it's a sitting duck.

Every single option is horrible, but for the short and medium-length term, the DPRK's least bad option is to continue it's military build-up.

Nuclear weapons definitely play a roll, but even if the DPRK had the best and most advanced nuclear weapons, the U.S. has them outnumbered to shit.