Most if not all of the US Navy was in the Pacific and there were enough defenses that the Japanese could not have taken Hawaii. The reason they could take much of Manchuria and southeast Asia is their defenses were mostly filled with pre WWI era weapons or had little to no defenses. They just blitzkrieged the entire place. Hawaii had significant modern defenses capable of warding off an invasionary force. Which is why Pearl Harbor wasn't a legitimate invasion. Japan just wanted to knock out US involvement. They didn't honestly want a long term conflict and take over like in "The Man in the High Castle."