It's not about surveilling China, it's about providing satellite coverage where the DOD needs it.

https://www.teslarati.com/spacex-starlink-us-military-500-700m-raised/

https://en.wikipedia.org/wiki/Iridium_satellite_constellation

See also Iridium.

SpaceX was contracted to launch all the Iridium NEXT satellites. All the Iridium NEXT launches have taken place using a Falcon 9 rocket launch from Vandenberg Air Force Base in California. Deployment of the constellation began in January 2017, with the launch of the first ten Iridium NEXT satellites. Most recently, on January 11, 2019, SpaceX launched an additional ten satellites, bringing the number of upgraded satellites in orbit to 75.