The situation in Korea is completely different. There are tens of thousands of jobs available, including white collar, but people don't want to work for those companies - everyone goes for the exact same handful of jobs, the very top. And because unlike in most of the West it's culturally acceptable to live with ones parents for 2 years while continuously applying for those jobs, that's what many people do. It's a tradeoff.

In fact, the parents often actively enable and support this strategy. Unthinkable in the West.

This is nothing like "I sent 300 resumes to every place in the country and can't get a job". Of course, such people do exist, but those are in majors/fields in which it was already near-impossible 10 years ago to get a job in most of the world. If everyone in Denmark would go "Maersk, Novo Nordisk, Carlsberg or bust", you'd see the exact same.

Honestly, your story indicates that your sister-in-law and her friends are likely at least middle class. Those who simply can't afford to sit around for 2 years (lower class) do just get a job straight away.