Short answer is that NK is pretty much self-contained. Occasional Kim might rattle his sabre but no one is too worried about it. Until they start making serious threats to the stability of other countries it’s just a case of leave well enough alone.

Sure it sucks what the people of NK have to endure but it’s not for other countries to tell them how they should live unless they directly ask for help or start threatening the sovereignty of other countries.

As someone else in the comments mentioned, WW2 wasn’t an intervention to protect the German citizens that were being persecuted, it was a reaction to German invasion of other nations.