It does not seem especially obvious that the price of a product should depend on the cost of its input and not on the value of its output? We can quibble about

It does not seem especially obvious that the price of a product should depend on the cost of its input and not on the value of its output? We can quibble about whether "time that a user spends listening" is correctly what a streaming service wants to buy from an artist, but it doesn't seem like the reasonable metric.