How much is a Masters worth?

I read this article twice trying to figure out why getting a Masters degree would result in a lower average wage than that of a simple three year degree.

One possible reason is the comparison is to others in the same cohort - the the same block of people who started university together. Holders of Masters degree would naturally enter the work force two or more years later and perhaps the wage gap is an artifact of this later start.

It is also possible that there are simply too many Masters degree these days- with most Korean's constant push for more education, perhaps the demand for Masters degrees doesn't match the supply.

According to the article, Master's holders are more likely to take the first job offered, or anyway, take easy-to-get jobs, while college degree holders are more picky.

About 55 percent of jobseekers with masters’ degrees or
higher tend to aim at jobs lower than their educational standing, the report
said.
Meanwhile, only 36.9 percent jobseekers with college diplomas apply for
jobs that are easy to get rather than what they want.

Some good news for those in my profession:"The study also indicates that college graduates with a B-grades minimum and a TOEIC score of 800 or higher find it much easier to obtain jobs after graduation." - Is that good news? I don't have much to do with TOEIC. Still, interest in English is interest in English.

I have been considering working on a Masters myself. I felt it would help my job prospects back home (whenever I do go back). Now, I wonder.