All Nippon (NH) doesn't have the scale of international network that JL has. NH needed Star Alliance and NH has publicly stated Star has brought in hundreds of millions (of yen) in revenue far outweighing the PR cost NH bears for Star in the Japanese market.
NH is essentially a domesitc airline and it has been scaling back international operations with the exception of their exposure to the China market.
I think JL has codeshare arrangements with all those partners in oneworld, Star and SkyTeam that just meet their customer demand and doesn't see the need so much to stick to one group.