More like tens of thousands. The Lazarus Group alone is suspected to be comprised of ~3,500+ people.
If I had to guess, likely because the NK workers are highly motivated to succeed under threats of duress and threats involving their families/own life.
I dont think these employers are willingly hiring DPRK workers over other countries, likely more so that DPRK are more ruthless and aggressive with their application applying processes and have it dialed in pretty well using shared intel and techniques to improve their success rates. Afterall, it is a nation-state backed campaign so they have a lot of resources to put into it.
But surely insignificant to the hundreds of millions in China, India, Indonesia etc.
Why DPRK when the alternatives are so much more numerous?
The entire population of DPRK is only 26mil, the entire country is half the size of the city Jakarta.
Most Americans probably outright lie on their CV, that tells you nothing.