ESPN would tell you it's because NBA teams need to have FIBA clearance letters and whatnots but I don't believe that a bit. The reason is purely financial; breach of Chinese contracts on their part would amount to about $1 million in compensation; plus undisclosed amount to both the Chinese agent and U.S. agent. With the exception of Martin, I don't think any import in China has even made $1 million in salary at this point.