Funding armies is expensive. Many western European nations have cut back since the EU is keeping them together and the red bear is not as strong as it use to be. It is better to have smaller active militaries with a large reserve and militias since you will be saving money that way.
Also China lacks the resources to get a large part of their army out of the country. The United States is literally a fortress. It is big, vast, has many cities, gun owners, military defenses, and big distances to drive.
