That isn't true, though.
Otherwise people wouldn't go INSANE for Tom Hiddleston, the Beatles, or Bendyback Cucumberpants.
Peoples tastes aren't all the same and fashions change. I wasn't implying that one size fits all, however markets reflect trends and fashions of the times they are in. Is it any wonder that D&D catered mainly to mainly men when they were 85 to 95% of the audience?
If you look at the art of Boris Vallejo and just assume it is sexist you missing the nature of his art. He frequently painted female body builders in powerful poses, not what would be traditionally considered attractive.
Although what I find funny is that I've been reading around the subject (looking at the back issues of Dragon mentioned in the OP article) and one of the letters that kicked it of wasn't a complaint about Spirit of Night, but actually in issue #111 about the cover of #109 which shows a rather dorky looking knight and it was the letter writers wife complaining there weren't enough "hunks" on the cover of Dragon.
Dear KM,
After we received issue #109, my wife pointed something out to me. She said, "When there is a female on the cover, she is generally scantily clad and well proportioned, but when there is a guy on the cover he is covered from head to toe and looks like a jerk."
I'm inclined to agree with her after looking back in retrospect. She would like to see some nice-looking guys on the cover — "a hunk." I have no problem with that. It might even entice some more women to get into the game.
#109 Cover "jerk"
#111 Letter about the lack of hunks.
#114 Spirit of Night.
#115 John M. Maxstadt letter complaining about 114 cover.
#117 Several responses to John M. Maxstadt letter. Some critical of it some in general support.
What I find interesting, is I didn't have to click back far to find this cover of a fighter in just a loin cloth and leather straps.
or this of a fully clad female mage.
In fact going back through the covers there isn't a huge amount of cheesecake, either male or female, the vast majority of it is just thematic. It certainly seems Spirit of Night was an exception, rather than common.
Semi naked male figures pop up more frequently than you would expect...
and fully armoured female knights aren't that uncommon either.
It does seem the original article is at worst cherry picking, or more likely suffering from some confirmation bias, or just the anecdotal evidence, where a few bits of controversial art are getting a lot of column inches at the time compared to the vast majority of art that was a lot tamer.