I can't shake off the feeling that behind all those reasonable sounding explanation lurks a lot of hypocrisy. No one has to hide shamefaced in a dark corner because he enjoys to read about a dogfight between two pilots;
Forget what the jargon term is for such stories, but there actually is something of a "genre" for this kind of thing. And it basically could be described as "excessively detailed act by act accounts of fighter dog fights"
a gunfight between gunslingers;
"Gun porn" is a thing.
a lengthy description of a difficult break-in;
Depending on the story and genre(crime), that may be a very appropriate thing to include. It's kind of like a "hard SciFi" story going into a very detailed description of the mechanics behind how a particular thing is possible/happening in the story.
but to read about people having sex is superflous.
If the story's major focus has little or nothing to do with sex, then having detailed blow by blow(literally!) accounts of sex acts is very likely to be superfluous.
It's either that or the author went "I think this story isn't going to do well on its own merits. So I better throw in a lot of sex scenes for good measure, and then market it under the erotica sub-genre as well." It still doesn't make the sex scenes relevant to the story line, it just makes the sexual content relevant to the specific genre the author was targeting.
Although all those scenes have the same potential to add to a story in regards to character development or to the plot. Or they don't add much, and a reader just enjoys the scenery.
Not going to argue that point, but in more than a few cases, it gets to the point with some authors, when those types of scenes come up, it's time to skip ahead a few paragraphs, check in briefly, and probably skip ahead several more, rinse and repeat, probably several times, until you find yourself 15 pages further into the book, at which point the story continues, and you've missed nothing for having just skipped over nearly all of those 15 pages.