You know how when you had analogue TV the picture used to get better or worse depending on your aerial, cables, interference, noise, etc? But your digital TV either has a perfect picture or no picture at all?
Same with audio over Ethernet compared to analogue. It’s the way Ethernet works. If there is audio at the other end at all, it is a perfect reconstruction of the signal. Any noise is not part of the signal and is ignored.
All Ethernet cables “sound” the same if they pass a signal at all.