Since the 80s you can spy on anyone's calls using the telco's standard maintenance features. You dial up a number, you then dial another number, and you're basically patched in to the second number, can listen in on any current call. There was a different system required by the government for taps, but linemen have their own method so they can diagnose issues. At least that used to be the case through the 2010s.

Stupidity and banality is a far greater threat than conspiracy.

Let's not overstate it. The US government hacks telecom for the benefit of the US government. Now having said that, as someone above mentioned, the intelligence agencies of the top 50 national governments are obviously all keen to use those hacks for their own benefit. And the flip side of that is that the US government is very interested in stopping these other national governments from succeeding.

Clearly, the counter-intel part of the US government effort has been less successful than the surveillance and intelligence gathering effort. But that doesn't mean that the US government wants all those other nations to be able to gather data from these systems. Our government wants nothing more than to be the only national government capable of gathering data from these systems.

Make your phone calls with Signal and you don't have this problem. So far the US government isn't forcing anyone to use unencrypted calling.