The DoD has far more than just 4 satellites up there.
Anyway, it’s vastly easier to destroy LEO satellites than Geostationary ones. A surprisingly tiny missile fired from an aircraft doing Mach 2 can take out Starlink satellites as you only need vertical speed the satellite provides energy at collision, but geostationary orbit takes significantly more. https://en.wikipedia.org/wiki/Anti-satellite_weapon
From the sources I looked at, NDSA is supposed to be less than 1,000 satellites by 2030 which isn’t a huge jump over what they already have. They just don’t benefit from that kind of satellite density at the bottom of LEO when it comes at the cost of lower lifespan.
What they want from NDSA is multiple different systems each with a separate focus that can all use a uniform transmission layer.
Anyway, it’s vastly easier to destroy LEO satellites than Geostationary ones. A surprisingly tiny missile fired from an aircraft doing Mach 2 can take out Starlink satellites as you only need vertical speed the satellite provides energy at collision, but geostationary orbit takes significantly more. https://en.wikipedia.org/wiki/Anti-satellite_weapon