Citizens of Nordic countries can move between the countries to study, work or live without restriction. No visas, residence permits or work permits are required. There would be no need for any of them to switch acquire citizenship of another.
I think population has a lot to do with that: Numbers roughly rounded but fairly represented. Canada is of course a big skating nation and it's very popular here but there isn't the population pool to draw from that there are in the other big nations. I'd flip it and say that despite the small population pool to draw from they are remarkably strong considering. But they aren't going to have that conveyor belt to pluck off of that others will.
Denmark, Finland, Norway, Slovakia, Ireland: 5 million
Sweden; Hungary, Belarus, Austria, Israel, Switzerland: 8-10 million
Belgium: 11 million
Australia: 23 million
Canada: 36 million
Ukraine: 44 million
Spain: 48 million
South Korea: 51 million
Italy: 62 million
United Kingdom: 64 million
France: 68 million
Germany: 80 million
Japan: 126 million
Russia: 145 million
USA: 324 million