Bach and the ubiquity of the power law

I have long been fascinated by the prevalence of the power law (Pareto distribution being a specific example) in all things human. It's there and yet it is hard to discern why it is there, or there so often.

Here is another instance. From Bach's Fifty Most Popular Works. It is based on the number of views of different Bach pieces on YouTube.

Click to enlarge.

OK - I see it empirically but I do not comprehend the causal mechanism. With so many masterpieces, why does it follow a power law instead of, for example, a linear decline?