Still talking about school Olympiads – Romanians get very good results with Olympiads (Sciences and Social Sciences), but not with chess. We’re likely not the worst in chess, but certainly not the first. And certainly we’re not dominating pretty much everything, as we do with Olympiads.
Chess is easy to practice by pretty much anyone, and you can get away with doing two things at the same time – studying at school and practicing in your spare time. Also, to some degree, natural ability matters.