This is also very relevant:
The ability to be preapproved, however, encouraged some Thais to travel to South Korea, find jobs and stay longer than 90 days while earning three to four times the minimum daily wage back home.
South Korea says these illegal workers led to social problems and that they engaged in criminal activity, forcing immigration officials to put Thai travelers with K-ETA visas through secondary inspections.
According to South Korean government data, there were 157,000 Thai nationals residing illegally as of September 2023, triple the number recorded in 2015. The government said last year that since 2016, Thais have accounted for the largest portion of foreigners staying in the country illegally. When the Thai Ministry of Labor in 2023 opened a channel for Thais staying illegally in South Korea and wanting to return home, 2,601 Thais registered.
Helps put it into perspective.