The lack of people to talk to is definitely the number one reason their English proficiency plunges after school/college, however in my rather limited experienc

The lack of people to talk to is definitely the number one reason their English proficiency plunges after school/college, however in my rather limited experience their reading isn't great. Like you say they have decent vocabularies, but they really try to avoid actually reading English text. I was working with some researchers for a couple of months and I was fascinated how they have their own world of scientific publications. You could be a totally competent scientists or engineer and not know a lick of English. They'd really only go to English publications as a last resort, and people I'd guess weren't under a ton of pressure to publish in English either. Since then I've actually noticed this is a trend in larger countries. There is some kind of critical mass of people which once reached makes them completely capable of living in a linguistic bubble. Mostly this is simply a question of how variety of media you have available to consume. Once it's high enough and you have the major western stuff dubbed, you can kinda cost with your local language. Compare something like Poland (where surprisingly few people speak English) and some place like Estonia (where everyone speaks English)