What if the jammer is on an UAV? In China’s case, multiple UAVs with GPS signal emitters can fly along the coastal areas and over Chinese fleets, safe from interceptions by hostile aircrafts. The signals emit by them can cause the GPS signals from satellites unusable.
The jammer UAV signals will also be in the wrong direction
Why use GPS signals from the direction of the Pacific when you have signals from:
1. the direction of mainland China
2. or which are clearly from space