The modern western concept of marriage is first and foremost based on romance. This idea, however, is not only a very recent invention, but is also somewhat illusory. We do not have to go far to find arranged marriages in parts of Africa and the Middle East to prove this point. Even in liberal societies like the U.S., one of the most important factors that people consciously or unconsciously consider in exercising their freedom to marry is the socioeconomic background of their partners. (The way that people exercise their freedom to marry again affects the socioeconomic class structures of a society. Check out this article for more information)
South Korea provides an interesting example for study because class-consciousness in marriages is much more visible than it is in its western peer nations. Consider, for example, the flood of advertisements from so-called "marriage information companies." As of 2016, the number of marriage information companies registered with the Ministry of Gender Equality and Family numbered approximately 1,000 (This number does not include the international marriage brokers which are estimated to reach 1,500). The average annual gross revenue of Duo, the largest marriage information company in South Korea, is over KRW 32,300,000,000. Check out the website of Duo U.S. branch here.
A 2013 study analyzed the records of 17,206 clients (8,154 men, 9,052 women) of a marriage information company, which included extensive background information of the clients and their families, e.g. education, income, job, property, and even appearance grade as evaluated by the company. The record also included the internal reports regarding the applicants’ preferred attributes of their future spouses, who met who, who liked who, and who eventually got married to who. According to the study, women considered men’s financial status as the most important attribute, whereas men put women’s appearance first. However, the study also found that there was a significant asymmetry between males and females in realizing their preferences. Men ended up marrying women whose socioeconomic background and appearance grade levels were both lower than theirs.
A cursory explanation for this phenomenon may be an unbalanced demand and supply - the sex ratio of people in their 20s in Korea has been around 1:1.1 in the last ten years. More fundamentally, however, the trend of female hypergamy (marrying up) is better understood in the context of a patriarchy. Either way, the practice leaves a group of lower-status males who are not competitive enough to find their spouses in the marriage market. The ones that exist way below the lowest grade in the grading table of a marriage information company.
Lower-class men who live in small rural villages are representative of such uncompetitive males. Apart from the individuals’ economic ability, the severe cultural and economic disparity between rural and urban areas puts these men in a vulnerable position in the mating competition. This is where mail-order brides come into play. In the ‘90s, with the municipal governments’ generous support and help from international marriage brokers, these men started importing brides from countries such as China, Vietnam, the Philippines, Cambodia, Uzbekistan, and Mongolia. The types of clients looking for the mail-order brides are slowly changing, though. According to a news article , international marriage brokers in South Korea report that international marriages are becoming more and more urban, with increasing numbers of better educated and better-off clients looking for international marriage services. However, most clients are still "on lower rungs of the eligibility ladder in a culture captivated by credentials, whether in looks, age or family connections." Some prefer foreign brides because they are looking for "a wife who can assume a more traditional role than one many Korean women are nowadays willing to play." Never the less, the sociology of marriage will stay valid, and the mail-order bride business, as well as domestic marriage information companies, will not disappear. Why is that? Just think about online dating apps and online mail-order bride services  in the U.S.
This post makes the "mating culture" in South Korea seem more materialistic than that of the U.S., doesn’t it? Let me just add that I do not actually know if same-class marriage tendency is stronger in South Korea than in the U.S. The relationship between marriage and class is a very tricky subject to research empirically, and it is difficult find reliable studies. Personally, I do not believe that class mobility through marriage in South Korea is lower than in the U.S. However, I do believe that South Korea lacks coherent, convincing, and powerful narratives concerning love, marriage, and family compared to the U.S. Lawyers, doctors, and business school graduates are likely to get married to their own crowd both in the U.S. and in South Korea. But it is more likely that Americans will have something to say like, "That’s because it’s easier to fall in love with someone who is around you, and whom you have more things in common with."
Culturally, South Korea is much more secular than the U.S. or Europe (almost 60% of the population don’t have any religion and less than 30% are Christians. The rest are Buddhists, but often moderate). The conservative idea of marriage in the sense of religion and sacredness is considerably weaker than the U.S. Instead, the conservative idea of marriage in the sense of Burkean social-order or in the sense of one’s expected role in an extended scope of family, is much stronger. Getting married is still considered a family decision to some extent, and the choice myth ("Marriage is a free, autonomous, and individual choice that one makes as a grown-up!") sometimes loses its strength in marriage.
Further, the development of capitalism in South Korea has been quick and abrupt, and there were no stepwise changes of trends in ideologies, unlike the U.S. or Europe. South Koreans’ belief in capitalism and meritocracy is weaker, or at least uneven, compared to that of Americans. As a result, South Koreans are arguably more acutely aware (and oftentimes unhappy) of their socioeconomic class.
My theory is that these all made South Koreans relatively blunt, or at least less embarrassed, about viewing marriage as a family-level economic deal.
What’s happening is also a side-effect of an institutional power. The institution of family. Historically, the institution of family in South Korea has long served as a system that assigned individuals a certain role and identity. For example, Yubokchin, a scope of family in which members were obliged to commemorate other members’ deaths by wearing special clothing, was known to have considered 136 different kinds of relatives in the 18th Century. Tens of appellations were used depending on who you were, whom you were referring to, and sometimes even in front of whom you were referring that person to, in the family.
To some extent, the sophistication and extendedness of family relationships in 17th to 19th Century was (and to a lesser extent, is) reflected in modern South Korean family law after World War II. Four different categories of family exist which apply differently to different family law rules. One of such categories is the family under the family headship system (hojuje). Remember the relationship between patriarchy and female-hypergamy? In fact, patrilineage, patrilocal marriage, and patriarchy used to be institutionalized in South Korean family and inheritance law until very recently (2007). Under the family headship system, the most senior man had headship of a family and everyone was required to belong to one family. The legal concept of family was determined regardless of who was cohabiting with whom in real life. Women belonged to her father’s family until she got married, and then was relocated to her husband’s family (or her father-in-law’s family, in case the husband was the eldest son of his father’s family).
The family headship system not only generated certain gender identities, locking women in the family and depriving them of power to represent the family at the same time, but was also an important mechanism that the state deployed to (re)produce its subjects (kukmin in Korean) by classifying them and giving different ranks and meanings to them. The cultural and social norms and the power dynamics that used to be institutionalized by the family headship system are still alive. In South Korea, the stigma against people who cannot or refuse to play their role in the institution of family is twofold: "First, the stigma against the so-called unfilial person who fails to continue the family line and second, the stigma against the disloyal kukmin who fails to perform his or her duty as a national subject." [The twofold stigma is quoted from this paper, which explains it in the context of LGBTI in South Korea.]
This explains a lot. It explains why South Korean men are sometimes pressured to find wives by their family, one way or another. It explains why many female marriage immigrants report violence and abuse from in-laws as well as their husbands. It also explains why the hell the local governments took the initiative in importing brides. As of 2007, 25% of municipal governments had some kind of policy that supported international marriage costs. Despite wide criticism that the governments are condoning injustice and sometimes illegality, some municipal governments are still maintaining such policies.