I would guess that people that are driven to risk their life to escape might be the ones that have the worst lifes and/or the most negative opinion on North Korea. There can simultaneously be a somewhat wealthy educated upper class in the capital (which would have little incentive to escape), and a very oppressed lower-class.
North Korea independently developed funcitoning ICBMs and nuclear weapons, you can't do that with uneducated starving peasants who are eating rats.
North Korea independently developed funcitoning ICBMs and nuclear weapons, you can't do that with uneducated starving peasants who are eating rats.