Well one of the things that China has to do is call in its debt and the u.s. economy will crash. They maybe China's largest importer but their economy has been a flat line with no good news on the horizon. they can't afford to have their debt called in.
1. Pakistan offers the following to China:
Direct energy access by passing the south china seas saving a ton of time and money
2. Cheaper and faster route to ship it's goods to the middle east, africa and europe
3. An extention of its naval power so that it can cut off america's oil supply at will in case of any tensions over taiwan
4. Same as number three for india in case of tensions over anachalpradesh
5. Pakistan will export it's own oil and gas directly to China since they are developing our energy industry as a part of CPEC (they get dibs on its export before anyone else, that's fair)
The list goes on and on.
You are going to fight USA for China. Not even the most brain dead general in the Pakistani army will sign up for that