The predominance of the surname Kim among Koreans is a result of historical and cultural factors in Korea. Here are several reasons why so many Koreans are named Kim:

1. Historical Tradition: According to historical records, the surname Kim can be traced back to the Goguryeo dynasty (37 BCE – 668 CE), one of the Three Kingdoms of Korea. Kim Chunsu (金春雨), a Goguryeo general, is considered the first person to bear the surname Kim. Over time, the surname became increasingly widespread and is now one of the most common surnames in South Korea.
2. Bureaucratic System: During the Joseon dynasty (1392-1910), a civil service examination system was implemented, and the surname Kim was favored by the ruling class. Many government positions were reserved for those with the surname Kim, which led to its proliferation among the elites. This practice continued even after the Korean Peninsula was divided into North and South, but to a lesser extent in North Korea.
3. Socioeconomic Status: Historically, the Kim surname was associated with higher social status. This perception has made it an attractive choice for parents who wish their children to be associated with success and respect.
4. Naming Trends: There have been periods in Korean history where certain surnames, including Kim, were fashionable. For instance, during the Joseon dynasty, there was a trend of adopting surnames that were associated with Confucian values, which further contributed to the popularity of names like Kim.
5. Immigration and Diaspora: The Korean diaspora around the world has also contributed to the spread of the surname Kim. Koreans who emigrated to other countries often maintained their cultural heritage, including their surnames, which has led to the Kim surname being present in various communities globally.
6. Random Probability: Additionally, the simple probability of surname distribution can also play a role. With over 70 million people in South Korea, random chance may account for some of the frequency of the surname Kim, especially considering that there are no family names that are systematically more likely to be passed down due to cultural practices.

It’s important to note that while the surname Kim is very common in South Korea, it is not the only prevalent surname. Other common surnames in Korea include Lee ( Ryu in North Korea), Park, and Choe, reflecting a diverse heritage and naming culture.