That's according to an article on Business Insider. Though, what's really the issue here is developed countries seeing a decline in birthrate. According to BI, South Koreans could be extinct in the next 735 years if the low birthrate trend keeps up.

While this is merely a projection, the birthrates there have seen some drastic and significant decrease. In fact, it's almost doubled and been on decline for the last 50 years.

“A 2014 study commissioned by the national legislature concluded that South Koreans could ‘face natural extinction by 2750 if the birthrate were maintained at 1.19 children per woman — assuming no reunification with North Korea or significant inflow of migrants,” based on data from the South Korean Assembly.

Between 2005 to 2010, 80% of South Koreans indicated they valued "Korean bloodline," only wanting to marry within their culture and ethnicity. That number fell to 65.8% in 2013.
This would give rise to mixed ethnicity, which the number of school-age children from that background has gone up seven times from 2014 to 2006.

Of course, this doesn't mean this will be an end to Korean attractiveness. And while this is a projection, hopefully it doesn't come to that.

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Do developed countries need to start making ads like what Denmark did recently?