I'm tempted to chalk that up to HN being, essentially, a pet project implemented in a toy language as a not entirely open source[0] forum maintained by volunteers. Of course, I don't know but that's my guess, that pg just didn't work very hard on polishing up the parts he didn't find personally interesting. For some reason, people seem to be weirdly elitist about HN's layout, and act as if any slight change to the UI is going to allow the barbarians of the internet to storm the gates, until Hacker News is aught but cat memes and ashes.
[0] The language and original forum are, obviously, open source. But AFAIK you can't make pull requests against the code HN is actually running, which has had tons of modifications made to it, because that's special sauce. There used to be a repo for making bug and feature requests but that seems to no longer be active.
Of course, you could roll your own minimalistic threaded forum, but getting people to move from HN anywhere other than lobste.rs[1] (if they want more moderation) or reddit (if they want less) might be difficult, unless you're serving some specific niche like DataTau[2].
[0] The language and original forum are, obviously, open source. But AFAIK you can't make pull requests against the code HN is actually running, which has had tons of modifications made to it, because that's special sauce. There used to be a repo for making bug and feature requests but that seems to no longer be active.
Of course, you could roll your own minimalistic threaded forum, but getting people to move from HN anywhere other than lobste.rs[1] (if they want more moderation) or reddit (if they want less) might be difficult, unless you're serving some specific niche like DataTau[2].
[1]https://lobste.rs/
[2]http://www.datatau.com/