how? Your theory of "Their fear of China is greater" and it's a result of that falls as soon as we take into account the history of US being present in those countries even before china became powerful. It was US who expanded in those places even before PRC was a thing and china was fragmented, weak, occupied.

Philippines: U.S. Colonial Period: the United States ruled the Philippines from 1898 to 1946, The Philippines was under American civil and military governance.

south korea: after world war two the divide of korea and US occupation of south korea militarily which is still present

japan: similar story as south korea