This seems overstated. Only a couple of countries were able to field a full team. Outside of Russia, very few countries were running two deep on medal contenders at any weight. Anyway, here is a good article on where the Olympic wrestlers actually come from. Transferring is straightforward and I bet it is not hard to read the tea leaves of your future in the Russian Wrestling Federation fairly early on. Wrestlers only transferred from three countries, one of which is Cuba and they are probably looking for something other than wrestling. For the US, my impression is Micic has strong ties to Serbia and would prefer representing them.