Oh shit yo, I recently did a major research project on human trafficking in the Philippines, which included taking a trip to the Philippines and interviewing NGOs and government authorities, and while you’re right that people do come voluntarily, a lot of people are in fact misled about what they’re going to be doing and how much they’re going to be paid for it. They have their passports stolen and women, in particular, are subject to sexual abuse. And that does count as human trafficking, by the way - if someone goes somewhere voluntarily under false pretenses and is in a situation where they can’t leave, that’s still considered trafficking.
Why do people keep coming? I don’t know about every country, but in the Philippines, working overseas is highly encouraged by the government. Approximately 10% of Filipinos are overseas workers. Working overseas is considered a goal for many people because you can make a lot of money and support your family.
I’m sure someone with more knowledge than me can elaborate, but essentially it is all an easily visible facade that is put up to portray North Korea as being a first world nation despite its crippling economic and political problems.
The Washington Post revealed quite a few indicators of their malnutrition crisis. And there’s this survey conducted of former North Koreans living in South Korea that shows 100% of those surveyed were tortured (presumably substantially higher than the rate of all North Koreans, but revealing nonetheless).