Not entirely true. My house was built with an A/V closet that's not in the living room. To put analog equipment (like a turntable) in the living room where it's used, I convert the analog signals into digital with a $100 A/D converter that sends them over CAT-6 under the house to a decoder that connects to the receiver with Toslink. It works great, and I bought this in the last three years.

Sure, for PCM stereo content it still works perfectly fine. Which is a lot of stuff! But it'd be a poor choice for 5.1 or better today.

I was curious about that; because I couldn't be bothered to do the math myself, I looked up the max bitrate of multichannel PCM. Found this at https://www.videohelp.com/hd :

"Linear PCM up to 9 channels (Max 27.648 Mbit/s)"

Cat5 or higher (especially only 20 feet) would easily handle that.