Pluss any fuel costs 100x the fuel mass on launch.

So you're sitting in your orbit and any changes (especially so close to the massive body) are super expensive. Which means sending anything after you must be pretty trivial (once the missile is already in orbit).

Spaceship just launched 30+ starlink v3 sats on its first orbital flight two days ago. It might as well have been flat disks of missile sats, even multi missile per each disk. Sitting there waiting, getting energy from solar, only having to expand fuel when a strong solar storm temporarily increases atmospheric drag on LEO + some minimal station keeping. A missile type sat with completely different budget for fuel and mass has a big advantage.

Maneuvering for a rendezvous (intercept), given 5-40 hours time, is very cheap in terms of ∆V (fuel used).