Because 역 is only used for trains and subways and 정류장 is used for buses, cars, and taxis. http://endic.naver.com/krenEntry.nhn?sLn=kr&entryId=ff798d0cf8fc4d42a42b9f2929a36be3&query=%EC%97%AD http://endic.naver.com/krenEntry.nhn?sLn=kr&entryId=1a31f27fd15647378ff6a4a052ee1485&query=%EC%A0%95%EB%A5%98%EC%9E%A5 A different word is used for different types of vehicles. Even though we use the same word (stop, station, etc) for both in English, if you think about it, a train stop or subway is quite different than a bus stop, so having different words for each does make sense to me.