Denaon - I wouldn't support this conclusion "There is no forum for the player", therefore: "he/the country has not achieved anything". Please don't see it like that. Do the most popular South American players have their forum? Yes! The only difference is that you find them in South America and not in a Chilean or Argentine forum.
To answer why the forum structure is as it is, you would probably have to dig a bit deeper and evaluate how it all started. Of course it makes sense to have the forum South America because lots of players are from these countries. And it wouldn't make so much sense to make a North American or Oceanian forum because the USA or Australia would be pretty much North America or Oceania in tennis, respectively. And it makes sense to do it with Asia, too. But I can't answer why there is no European forum
I think it would be worth discussing about this matter. We can break up the whole South America complex and give Argentina, Chile and Brazil their own country forums.
The it would look like
Losing the "South America" category would mean a thread about a player from Uruguay, Peru, Colombia, Paraguay etc would need to go into the "other world" category, right?
Or do you want to keep the South America category and only make additional subforums for the countries.
example: you want to go to Nalbandian, then you would click South America(old) ---> Argentina(new) ---> Nalbandian(old)