Is it? We actually don't know that as a fact, because the conventional wisdom was that Iran would get flattened in 2 days yet it took out 5 confirmed THAAD radars, 1 PAVE PAWS, and potentially 4 replacement THAAD radars, including some stripped from South Korea itself. It is having immense effect on Israel despite using only drones and MRBMs.North Korea's military strength is actually inferior to South Korea's, and neither Russia nor China would send troops to support a potential offensive.
Furthermore, Kim has shown no interest in this, because he knows it's impossible; the "two-state theory" serves as a case in point.
The problem is one of exploitation and North Korea's proximity solves that problem.