This goes for many jobs in South Korea -- they simply don't want foreigners to do it, because foreigners aren't Korean. The exception is teaching English Conversation, because the Korean teachers very obviously can't do it well enough themselves. The government is trying to limit South Korea's reliance on foreign ESL teachers though.

This goes for outsourcing too -- the UK government is happy to consider having foreign companies build nuclear power plants or railway lines in the UK, but the South Korean government would rather have everything in South Korea done by South Korean companies, even setting up a company to do it if necessary.

When Westerners open their labour markets to foreigners and foreign companies, what can they do if the foreigners do not reciprocate?

Americans get more goods and services, and have to work less to get them? How is this not a net benefit to the US?