If you look at the history of the WW2 Pacific theatre, you would notice an apparent lack of Imperial Japanese Navy activity between Guadalcanal and Philippine Sea. And even these two battles were reactive in nature (in reaction to US moves). The last proactive Japanese operations were in fact Midway and Aleutians in June 1942. Therefore, for more than a year IJN practically did next to nothing, although they still had plenty of powerful warships. What would be the reason for that ?
So far I have heard two explanations: One is that the Japanese waited for a decisive battle (Philippine Sea was supposed to be that), and conserved their strength for that. The obvious flaw of this strategy would be the US's industrial capacity, i.e. the USN fleet was growing much more rapidly in the same period. The other reason would be the lack of fuel. Apparently the Japanese were in such a bad fuel situation that they didn't have much choice than to sit and wait for the aforementioned decisive battle. Fuel explanation seems flawed, because IJN had high operational tempo in 1942, even in early 1943 but then it all stopped. Also, even in 1943 and 1944 they were moving ships between bases in Rabaul, Singapore and Japan proper (which did use lots of fuel). I don't deny fuel shortages, but they do not look so severe in this period to justify complete lack of action.
Considering the vastness of the ocean, and inability of the USN to be everywhere, neither of these two theories explains why the Japanese did not mount some smaller-scale hit-and-run raids against less defended targets to keep the Allies off balance, involving perhaps forces consisting of one smaller carrier like Zuihō, a few heavy cruisers or fast battle-cruisers and accompanying destroyers. This would not have risked the heaviest major units of IJN, but would have given the Japanese some sort of initiative in the war.