Why do people gatekeep?

I’m Korean-American and have been living in Korea for a bit after moving here recently. I grew up in a household speaking Korean but am far from fluent and my accent isn’t great either, so I’m actively trying to improve. So far I’ve met a few other Korean-Americans and some of them speak both English and Korean perfectly and have native-sounding Korean accents even if they grew up in the US. I have asked for tips on improving or how they became so fluent/developed such a good accent, but all of them have given me vague non-answers or straight up told me they don’t know and then quickly changed the subject. This is something I’ve noticed with many Korean-Americans I knew in the US, too; when I ask them how their Korean is so good, they just say something extremely vague and then brush me off. I genuinely don’t understand why people do this as I’m just trying to learn how to become better at the language and it’s honestly very surprising and disheartening. Why do people do this, especially so many other Korean-Americans I meet?