Simply hearing the message "you're not free in your country...get out" is far from enough for the average person. They are completely inundated from birth with worship of the Great Leader.
There's an awesome book called "Mig Pilot" by John Barron that details the story of a Soviet defector in the 80s. He talks about how he believed everything from the US was actually propaganda. He didn't even believe the grocery stores were real. It's a fascinating read.
North Korea punishes your whole family if you misbehave.
If you're a North Korean hacker, you're probably living better than 95% of the country. You and your family probably get to live in Pyongyang and get good food, housing, healthcare, opportunities for your children, and so forth.
Why would you risk that? What could you, as one person, possibly do that would have any chance of success in fixing your country? The only thing you would get is your whole family thrown into a labor camp for the rest of your lives.
There's an awesome book called "Mig Pilot" by John Barron that details the story of a Soviet defector in the 80s. He talks about how he believed everything from the US was actually propaganda. He didn't even believe the grocery stores were real. It's a fascinating read.