It’s the fault of the creator and the community and is on purpose. This site is meant to be for more intellectual discussion and not cheap quips. If you want threads full of one sentence and derailing comments you can visit Reddit: this site is engineered to /not/ become like Reddit.
It's not really fair to pin "fault" on anyone in particular for the culture that develops on any given social media site. These things just kinda emerge.
I think hn itself is a counterpoint to your assertion. The toxic culture hasn't really "emerged" here as it has on countless other platforms, due primarily to ruthless call-out/moderation/shadow banning etc.
Humor isn't toxic. What's toxic is the vituperative snark, contemptuous elitism, low-effort cynicism and outright hatred this community breeds and that dang constantly has to put down because (among other reasons) we have to be pedantic humorless prigs about everything.
I'll take more dumb jokes over yet another diatribe on how Twitter's latest moderation policy changes will lead to mass graves and white genocide any day.
I didn't mean to imply that the particular cultures of the various social media websites are "toxic", they're just all different. Each site has their own style of talking, peculiar grammar rules, appropriate topics, and memes, and all of those things exist on HN too, at least to some extent.
HN post topics are restricted, usually to technical stories or less controversial political topics. Comments tend to be precisely worded, and are often more pedantic. Because of how linking works (or rather doesn't), citations often use a particular format. Comedy is generally discouraged, though is accepted more if (like in Traster's top-level comment in this thread) there's also "legitimate" point attached. If that comment hadn't included the second paragraph, it would probably have been downvoted. All of that is part of the culture of HN, and I wouldn't necessarily call any of it toxic. Some of it follows directly from the site rules and moderation, some follows from the technical limitations of the site, and some just emerges from the sorts of people who happen to use the site.
While occasional humor is welcome, if we reward it too much, then the comments will be full of low-quality jokes. I think most readers here aren’t looking for that.