These medal winners found success after switching countries they represented. The leaders of their old Olympic federations are no doubt biting their nails.
The Olympics is about the individual athletes, not nations who compete in the medal tables. But athletes who change their citizenship to compete are referred to as "passport Olympians" or "Olympic carpetbaggers," and it is a tradition that dates back at least as far back as the 1920s, when Britain fielded ice hockey teams made up largely of Canadians. Perhaps these terms are unfair, since these athletes do care for their newly found homes. Anyway, life is complicated.