Well, that’s because I am a Korean descendant, and in accordance to the laws established in your country my visa allows me to get any job in case the employer agrees that my competency meets the requirements of the position offered.
Another possible reason is that there is a deficit of native Koreans who are like yourself despite of the decent level of English that is probably sufficient for teaching never heard of the things called “manners” and are ignorant enough to judge a person by the country of origin.
Hope I answered your question. Please, your willpower to resist from further comments is highly appreciated. Thank you.