Why does FM radio sound so good?

Wisconsin Public Radio has an outstanding signal especially at home base in Madison . Took a tour thru the studios a few years back, thought
maybe those 8k pro Tascam CD players had something to do with it .
I know the least compression possible did .

lowrider57

Carts were clunky, but the later generation of tape decks used to rec/playback were first-rate. When making a promo or any recording, you would hit a button and a cue tone would be recorded into the tape.

Yup! The best cart machines had very high SQ. Carts also used a "tertiary" cue tone that could trigger a flashing light (very helpful on Top 40 stations to mark the vocal post or the approaching end of the track) or to trigger another machine.

I don't listen to a lot of FM these days. But when I do it sounds as 'clean' as ever. It does not have the frequency response of a class vinyl or even the best digital. So I figure as I age, I don't hear much more that what FM is capable of anyway. But the best stations, actually have some depth and space to them. 
In contrast to the horrid compression of satellite broadcasts. 

Classical and college radio sounds excellent thru my home system; clean is a good way to describe it. I’m using a vintage Denon tuner.
Rock stations sound good as well, except for the loud compressed bass.

FM music is soo good before digital.