Here's a map at conclusion of IJN (Human) victory over Allies (CPU). Sea lanes win.
I'll give the AI credit for at least recognizing the danger and making concerted attempts to "open" the lanes. Allies successfully took Samoa, and then threw a good bit of effort into trying to take Fiji until time ran out.
Would it really be that hard to program an additional layer of AI "thinking". The AI knows it must take Fiji (or at least destroy the base). A simple trace program between the desired target island and major IJN ports would identify Tarawa as the key link. A successful Allied invasion of Tarawa, would isolate not only Fiji, but the entire sea lines island chain.