Maybe so, but I actually think it's more of an issue with intermediate level teachers.

At beginner levels in a non-native environment, like Korea, students don't have much exposure to English to acquire working knowledge of grammar use. So, many teachers explain language using L1. However, there comes a point when students could benefit from learning English in English. It's at that point that teachers who have become comfortable with using L1 (even native English speakers) might rely on it rather than English only.

Where are you teaching, Steve?