It doesn't need much of a theory to me. People who don't understand the engineering involved are being taken advantage of by charlatans selling phony products with explanations that almost make sense at first glance and induce a placebo effect due to that and price (so they do "sound better"). The audiophiles (and likely some amount of sellers) naturally try to defend their purchases, but they're trying to reason based on the nonsense they were sold, and end up in a feedback loop of nonsense. People getting older and trying to reclaim their faltering hearing probably plays a part in it too.