To say something in favor of music: if well done, it can support the story and mood very well, improving the experience, at least for me. In any game (not only AVNs) I usually stick to the default music if it at least halfway makes sense and fits the scene. My "own" songs I can listen to at any time anyways.
However, if you just give me the same song on a loop or even a selection of songs which will just play regardless of the scene and situation, that is indeed useless. And I will agree that I also don't need music for these games. But, as I said, if well done it can really improve the experience.
(First things I do when playing a RenPy game is activating fullscreen and instant text speed)