Music is just layered simple patterns and our brains LOVE IT.
Sound is pressure waves, musical notes are a specific pattern of pressure waves. Melodies are repeated musical notes. Songs are repeated melodies following standard structure.
Our brains love trying to decode and parse all these overlapping patterns.
Maybe not really a shower thought and more wild speculation.
Listening to the same song over and over is no longer for enjoyment, it is for the feelings of safety that your body is comfortable in.
No, that is definitely for enjoyment