Why is Korea a hierarchical society?
Hierarchical societies are in fact common among societies where agricultural resources are scarce and can not feed an entire population.
Korea used to be an agricultural society until about 40 years ago. Since most of the country is made up of mountains and land that can not be cultivated, very strict rules governing society were needed in order to avoid internal conflict. Within families, since harvest was sometimes scarce and very vulnerable due to climatic conditions, there had to be a leader in families and in societies to decide what would happen in case harvest failed.
Confucianism only partly codified these hierarchical uses, parts of those codes evolved, others were ignored and others were adapted to local circumstances. It was decided that hierarchy would be based on age rather than any form of merit, since Korea is a homogenous land with similar topographic features in most parts of the country, and it was considered that farming was learned through experience rather than ability. Of course, those who failed to be good farmers were outcasted regardless of age, but in order to prevent a race to who would control land and production, older people would teach younger people.
These principles did not evolve when Korea moved from an agricultural to an industrial society. Economic development was so sudden that they could not have changed overnight. Social codes evolve over years and only economic, military and natural needs make those changes evolve (natural disasters, war or economic change) produce such changes.
Since things have worked out for Korea so far, Koreans are convinced that hierarchical systems work. In fact, since Korea is still a relatively homogenous country in economic terms, if there were a merit based system, the competition for who would get to the top would be fierce and conflicts would arise. As for hierarchy, one needs to understand that few Koreans are actually in control of the economy, and they don't want other people telling them what to do.
Regarding respecting teachers, in agricultural soceties where resources are scarce and harvest is not guaranteed, listening to those who will teach you farming is essential. As for parents, since they were often those who taught their children how to farm and provided them with the little food that they had, respecting parents was viewed as important. Religious authorities, shamans or anyone who was believed to communicate with nature was respected because such people could guarantee better harvests.
Western societies either have diversified economies and agricultures or small populations or both, and therefore do not require such strong hierarchical systems to govern society. To each according to their needs...