Dude Japan has no desire for war, or even to aggressively pursue its interests. Burden that with an ageing population, poor growth and the fact the Japanese need to modernise and build their land and air arms, the last thing they will do is join a war. They already went down that route and it didn't end well. I was shocked to see they have lowest percentage of young folk who are willing to fight for their country.
The Philippines? Duterte has just finished his "turning point" visit to China, that's the end of that.
Vietnam will fight to protect territorial sovereignty, not join a collation of countries against the Chinese. Do remember they share a large land border and will have to forever worry about when everyone else either tires out or walks away from the war.
The US, yes you have a point but public opinion now wants disengagement with the whole world police thing. Why do you think Trump has had such a good run? Hilary will probably be the last of the hawks who wants to take it to various countries, the US public simply does not want the commitment of its sons and resources to parts of the world which do not effect the US directly.