Coal is for national defense. It's NK's main export. He's not bombing them with bombs, he bombs them with low coal prices. It's easier than enforcing sanctions and we get electricity.
NK is irrelevant, and has nothing to do with national security. Those plants were going to shut down for being economically unviable.
Once the price of coal goes down due to a flood of new supply the power plants are suddenly viable again AND North Korea's biggest cash cow dies. Pretty brilliant if you ask me.
Economically unviable yes, because the price of coal was too high due to low supply. That's DC fascists "regulating" the market. So rolling back those regs is a double whammy.