And now I’ll wait for Mike the Musicologist to jump all over me.
(One criticism I anticipate that he might make: it isn’t just metal that corresponds to economic development. Which is a valid point. Generally economic development = more leisure time = more time to make music for fun and profit, as well as more places to do so. It’s hard to make music, be it metal, punk, rock, soul, or folk, if you’re spending all your time sunup to sundown trying to scratch a bare subsistence living out of the earth. I think what the author is trying to say, though, is that it takes more resources to support a metal band than it does two folksingers with acoustic guitars in a coffee house.)