I think the coordination with the highly depends from the age when that kid started to make any kind of sport activity and how is the countries education system organized (how important is phisical education for them). Of course it is also an ability which born with the person itself but can be largly altered in most cases by starting sport in early age. And now I do not mean professional volleyball but any kind of ball games for example.
I also agree with the fact that till for some countries' players it is a way to have a better level of life and can live from that money what they earn so many player consider it as a goal and do not share their energy with studying and sport untill the other countries where the level of the life is maybe a little bit higher and professional sport does not give a pro athleet lifestyle options, the players will prioritaise studies and so less time for sports. I think this can largly effect the efficiency of that countries sport on international level.
Also we know differences between for example a sweedish and a russian/serbian school...
This part of europe also "lucky" to have rich history (many nations were leading these area - German/Austrian/Hungarian/Russian/Turkish and so on I could write many more) so it is not so usual anywhere else to have such a variety of genes which also can help in having good abilities in sport genetically.