Realism and history are not the same thing.
Realistically, those pacific islands are not worth much. Historically, Japan invested a lot into defending them. Which was almost certainly a mistake and a very poor use of her resources. In TripleA, players have perfect information and battles are simple probabilities. Do you want players to fight over these islands, like happened in history? Then make fighting over them worthwhile.
Its not a mystery than players will give attacking a territory worth 6 a higher priority than attacking a territory worth 0.