You silly, you watched anime and drama with English subtitles. That's the same as reading English. I've read so many English books in my life, why can't I read Korean? Doesn't that sound pretty dumb? Exactly. Turn off the English subtitles (or whatever language that is not Korean).
No they didn't. If they put on blindfolds and earmuffs while they were learning Korean, would they have learnt Korean? I think you know the answer. We acquire any language through comprehensible input only. No exceptions. If you know anyone that learnt any language through speaking, please contact any linguisitics professor. You have just found the first case of language spontaneously occuring in humans.
They woke up to an American alarm clock. Drank only American beer. Listened to American podcasts. Drove an American car. Only spoke to Americans. Only learnt how to say hello in Korean. Didn't even bother learning Hangul. They didn't live in Korea...they lived in America. It doesn't matter what country you live in, what matters is how much Korean enters your brain. You could live in complete isolation in space, immersing in Korean 24/7 and absolutely DESTROY someone who "lived" in Korean for 10+ years but didn't bother immersing.
Then don't lol. Go to "r/Korean" or "Bo Gilly" and give up on Korean after a month of textbooks and speaking. I may not be close to fluent but I've absolutely reached a much higher level in a year compared to people following traditional methods. It's not just me. Everyone I know who follows input-based methods absolutely destroy people who've been using traditional methods for years. This is not a guide for going all the way to the finish line, this is a guide to get you started so you can actually learn Korean the right way. The earlier you start immersing, the earlier you can start learning Korean. I've failed so many times before I found immersion, so it is my mission to empower Korean learners to learn Korean the right way.