Part of it might be due to the rise of static site generators which almost by definition do not directly support comments without having an additional non-static service, external or not.
Even just having an endpoint to submit comments seems a lot to ask when the site otherwise doesn't even need a database.
Ultimately I think the need/want for discussion is better served by different websites rather than asking every site to provide comments. It would be nice if browsers could integrate or at least link those comments for you.
There are a number of commenting solutions that work with SSGs. Two in particular which may appeal to the HN crowd are Utterances[0] and the more recent giscus[1], each of which uses GitHub services (GitHub Issues and GitHub Discussions, respectively). Assuming your commenters don't have a problem with having to log into GitHub to say something, either of these will work. I've also written in the past[2] about some other SSG-friendly possibilities.
It's been up for almost a month and I already engaged one person. That's less than discussions on Mastodon, but it serves as an obvious meeting point for readers, so I guess it's not entirely a wasted effort.
Even just having an endpoint to submit comments seems a lot to ask when the site otherwise doesn't even need a database.
Ultimately I think the need/want for discussion is better served by different websites rather than asking every site to provide comments. It would be nice if browsers could integrate or at least link those comments for you.