I see what you're getting at, BUT... when most of those singers were thriving and coming up (aside from maaaybe Alicia Keys) there was a *legitimate music press* that covered musicians. So, really, they didn't need to be on Vogue or Harper's Bazaar or whatever to promote their albums. I mean, I'd almost say it's a similar thing with movie stars. How many of them were ever on Vogue when those old-fashioned *film industry* magazines existed to promote themselves? Enough that you could probably count on one hand.
I do find the talk of "so and so" should have had a Vogue cover to be silly, like.. not everybody can be on the cover, come on. Not everything is a snub. There were legitimately more publications and magazines in print back then!! It's silly to complain about Aretha Franklin not getting a Vogue cover when she was on the cover of Time, lol, a way more *impactful* magazine than Vogue in the 1960s (sorry!!!).