Because we're Korean. :) In all seriousness, it's a Korean tradition. Here's a part of a Wikipedia article about it: "Korean women keep their family names even after their marriage, but their children take the father's surname. In the pre-modern, patriarchal Korean society people were extremely conscious of familial values and their own family identities. Korean women keep their surnames after marriage based on traditional reasoning that it is what they inherited from their parents and ancestors, and cannot be changed. According to traditions, each clan publishes a comprehensive genealogy (jokbo) every 30 years. However, it is not uncommon for women to be addressed with their husband's surnames after marriage. There are around a dozen two-syllable surnames, all of which rank after the 100 most common surnames. The five most common family names, which together make up over half of the Korean population, are used by over 20 million people in South Korea."

@josep If I were to take my husband's surname, I wouldn't feel like his property. It's not supposed to mean a husband owns his wife; it's supposed to symbolize them becoming one family with one name. I assume because the countries you named used to be completely patriarchal is why the husband's name is typically taken rather than the wife's. Although, some women DO choose to keep their surnames; just as well, some men change their names to their wive's. It's just not most common. :D

Women all over the world often keep their own surnames.

didnt know koreans women keep their own surnames and it seems good to me. In my country women never change their own surnames. a "Lola Garcia" will be a "Lola Garcia" all through her life whatever her marital status of else. Never understood why in so igualitarian, developped and democratic societies like USA, UK, CND, Sweden, etc women accept it without a saying! I have the impression that it is a myth that women in those countries dont feel like becoming a "property" of a man! if you dont mind, tell me if i m wrong!.