They’re always sealed to people trying to escape.
North Korea is a giant cult focused on a dead dictator and his dead father. The people would revolt in the blink of an eye if there was someone still sane within the NK army willing to call for an end to the regime. I know nothing about the son who is going to replace him, but it may be less a matter of him having the ruthlessness to continue the dictatorship and more a matter of those around him (who have a vested interest in continuing the enslavement of the North Korean people) forcing him to be the face of a despotic regime.