I think this tracks in most adults who learn a foreign language. Within six months of moving from the US to a Western European country, I could read and understand enough spoken language to get through the day (commuting, groceries, restaurant, etc) and since then I’ve met a lot of people who have been here for a decade and still struggle with those things. The difference I believe was that I was highly motivated.
Not to toot my own horn, but I moved solely on my own accord. Sure, I have a work visa, but that was for convenience, not necessity, whereas many immigrants come for a short term job that turns into something more or because they are fleeing from war or disaster. I entered with the mindset that I need to learn the language and putting it off is just hurting my future self.
When people ask me how I learned so fast, I told them the truth. I don’t have much else to do in my free time so I “study”. These days, I even browse Reddit in my target language. I believe people are really quite capable of learning language, especially adults! But it requires intentionality and practice be develop proficiency, like anything really. If you want to get good at languages, you have to speak, read, and write every day.
To bring it back around, many of the best English speakers I have met engage parts of their life in English that they don’t need. Leisure and entertainment are the top contributors but depending on your profession, it could be required to speak/read English at work as well. It goes to your point of how the excellent students learn and I think everyone can apply to these ideas to learning across a wide range of topics.