Because the United States isn’t the king or general of the status quo coalition, it’s the ‘team captain.’ If it proves to be a bad team captain, the team may well choose a new captain, or disband altogether, with catastrophic implications for American interests.
I can't imagine another 'team captain' suddenly forthcoming. If Britain got its head out of its ass and regained that imperial edge, then maybe, or if China suddenly underwent a democratic revolution and reentered the world stage as a liberal power.