The population is not dumb, people are just trying to make the best out of the situation. Like when they had some reporters go to a village, where women were sewing some clothes:
Reporter: "Do you like the life in the country?"
Woman (in subtitles): "We do what we can"
Guide-translator: “We do the best for our nation!”
If they could, they might revolt, but NK is really well structured to prevent that… and even if they run away to the South, they find themselves in a modern country with no hireable skills.