Sallyann1234,
I think the main driver is we get the orbits, frequencies and ground stations up front.
The 90 satellites are useful, the military always need bandwidth for voice and data and, if you remember, the US snapped up Iridium and never looked back.
For the future, cubesats are packing more and more in and a single satellite could serve multiple functions for commas, navigation, Elint etc.
Evrybody has an idea of a large satellite with large aerials - but to give an idea of how small - and I mean very small - a modern satellite transceiver can be, see here...
https://www.inverse.com/innovation/s...et-transceiver
As for GPS, as long as you have a ground station you have triangulation.
https://www.c4isrnet.com/battlefield...-a-gps-backup/
https://digitalcommons.usu.edu/small...S6NextOnPad/5/
https://digitalcommons.usu.edu/cgi/v...ntext=smallsat
https://spacenews.com/first-hawkeye-...nting-signals/
https://www.seradata.com/hawkeye-360...on-from-utias/
https://www.sbir.gov/node/1620975