Likely the cable gets physically damaged, which degrades the signal integrity on the cable. Basically if the cable is cut there will not be any signal anymore,

Likely the cable gets physically damaged, which degrades the signal integrity on the cable. Basically if the cable is cut there will not be any signal anymore, but there can also be states somewhere in between. With reduced integrity the chance of data loss or corruption during transmission increases. There are typically low level integrity checks and forward error correction used to compensate for some of that on serial links, but they can only do so much. If data is detected lost its pretty much up to the upper level protocol on what to do next: One could retransmit, do nothing, or just use the corrupted data. Since retransmission would not help audio protocols they likely will use the other options, and so you get degraded sound.