[Sharlin]

Microwave relay links predate spaceflight and even when comms satellites became a thing, it made (and still makes) little sense to beam regional TV/radio/phone up to geosynchronous and back, due to cost and latency. There was no good replacement to terrestrial microwave until fiber optic became a thing.

In a very real sense microwave relays are the direct descendant of the optical telegraph (aka "clacks" in Discworld lingo).