Greil Marcus answers this question. “Dear Greil: I have two 17-year-old students working on a podcast, trying to understand what ‘Classic Rock’ is. Is it ‘white-guy music?’ Is it just marketing? Is it just rock and roll? Who decides what is and isn’t?”
Classic Rock is what you said: Marketing and White-Guy Music. It’s a strategic concept meant to enforce a narrow worldview and shrink an historical episode into a segment of radio programming that could compete in a fragmenting commercial landscape where Top 40—which is to say a radio republic where most people, as being exposed to and with access to the same music, could make their choices and argue about them with other people, speaking a pop lingua franca—was being replaced by an ever-more diced-and-sliced formatting of AOR, Easy Listening, Heavy Metal, R&B, Disco, and on and on in a radio landscape where people were presumed to have nothing in common and nothing to say to each other, which was also an argument about the United States, and then the world, as such. Classic Rock was invented to sell a concept to people of (mostly) a certain age to reinforce an identity that could be further mined to segment commercial choices of all sorts: in other words, if you could profile the sort of person who wanted to hear the Rolling Stones’ “It’s Only Rock ’n’ Roll (But I Like It)” you could also—and this is before algorithms—commercially profile them in terms of residence, shopping, car ownership, and so on. To rationalize this, that meant even further segmenting, leading to such perfectly predictable phenomena as the Classic Rock Weekend programmed for Classic Rock Stations all over the country across a certain weekend where something like two or three hundred informational segments, on, for example (I will never forget this), “Stevie Nick’s Writing” (yes, I know it’s “Nicks,” someone entered it in error or didn’t know), and out of all the programmed elements, featured three on black musicians, all of whom were Jimi Hendrix.