I think the reason Japan only hire naturalized who only plays for their domestic league (B league) due to availability.. Japan can hire NBA talent naturalized players but availability is also the question mark for players who are NBA based... Same reason why Tim cone picked Brownlee over much touted Clarkson because of familiarity and availability.. Japan having hard time choosing naturalized players because most of imports playing in B league are adjusting to the system of most of B league teams who are playing within the system... So, those imports limiting their ability to take over because they have to adjust to play within a system.. take example is Jonathan Williams, he is PBA's current best import last season, but when he played in B league, he look like ordinary baller because he has to play within the system, even he can takeover.. Although he's not played in B league but same scenario, RHJ played in Korea and he's not effective there, when he played here, he gained momentum, become a PBA champion and best import awardee, thus, Jordan picked him as naturalized player then become integral piece of Jordan national team..