Why the strong focus on Russian/Ex-Soviet cities in the article, though? It seems odd that there is a detailed list of present-day closed cities in Russia but only passing mention of other countries.
The most likely explanation is because that's where they were the most prevalent or most well-documented. The lead of the article notes: "Closed cities are a feature of heavily militarized countries and secretive regimes, and many still exist in the successor countries to the Soviet Union."
Or it could just be that whoever added the content has Russia-centric knowledge or interests and contributed that. Wikipedia knowingly suffers from systematic bias [0] and many articles will have a tag like this one [1] for being too US-centric. The problem with addressing that is that most editors are American and don't really have access to other language reliable sources. Though in this case the sources are in English so it could just be that English-language sources all focus on that area.
