Not sure if this is facetious, but HN does have a rule that prohibits editorializing. From the Guidelines: "Otherwise please use the original title, unless it is misleading or linkbait; don't editorialize."
No, I was genuinely asking because I had found many HN posts were editorialized.
Maybe HN should auto-pull title from URL, and then add the posters title as a form of "subtitle/comment"
This assumes those titles are usable, which they often are not.
Populating the field automatically might nudge people toward doing the right thing, though.
Half-joke: HN scrapes first few text lines in HTML (in case the very first one isn't the title) and one of them has to be used as the title.