The reason should be obvious. Digging long distance trenches and all of the property buying/leasing and right of ways/easements and all of the other fun stuff makes it a total nightmare. Radio broadcast just makes much more financial sense as well as logistically.
Had "the second longest T1 in the service area" for a while there. BellSouth declined to renew the contract in 2008, the business folded, etc. In 2013 I was digging through the old building, and the T1 line card in the wiring closet was still powered.
Nowadays the relay boxes all the way into town are mostly hanging open or have been repeatedly run over. I wonder how much of the rest of that infrastructure they just abandoned in place.
How do I know? Well, we had a pretty big wildfire a couple years ago that burned a microwave tower a couple hours away. The official response was that they couldn’t get internet back in town until they rebuilt the tower. Our internet was down for a couple weeks until it was safe enough for them to get back to the tower site.
In a very real sense microwave relays are the direct descendant of the optical telegraph (aka "clacks" in Discworld lingo).
Its a radome, used to protect the antenna from weather.
Those microwave links represent layer 0 in the connection which is by definition always analogue, the same is/was true for T-1 which used alternate mark inversion [1] signalling over a 4-wire circuit. It is the type of signal carried over the link which decides whether it is considered "digital" or "analogue". T-1 carried 24 time-divided PCM channels ("digital"), microwave links could and can carry both frequency-divided multiplexed analogue channels ("analogue") as well as time-divided PCM or packet-switched channels ("digital").
[1] https://en.wikipedia.org/wiki/Bipolar_encoding#Alternate_mar...
This is misleading. The phone network used analog links (typically microwave relay) for long distance almost exclusively for many years (into the 80s) after the introduction of T1. T1 itself is not terribly well suited to very long distance links though and can only be pressed into it with repeaters every mile or so.