However, if later down the line we create autonomous agents that can initiate the creation of said music themselves then I'd call that enough agency to say that the machine is "making music". Could probably almost do it now; tailored LLMs, image diffusion, music diffusion and you could have an ML agent that acts as a musical artist; posts to instagram etc with images of their persona "working on something new", releasing new tracks, bantering, etc. There are already AI OF stars apparently.

We could say "yeah but a human still set it up and told it to make music" but I would discount that; pretty sure no human has total agency, we are all impacted by our environment, peers, culture and all sorts of other external influences.

And I don't think sparsity changes things (maybe in the material world) but culture certainly does. Things are popular because they appeal to us in bulk, rarity/sparsity always result in higher effort for the payoff and so decreases popularity.