Part of the reason is: while I am thoughtful, reasonably well-informed individual, I never felt up to the task of putting in enough effort to create an HN-worthy comment. This was inspired almost entirely by the _quality_ of the kinds of comments that I saw over the years -- at least for the kinds of posts that drew my attention.
- Many (most?) of the comments were made by experts - They often included disclaimers, especially when the poster considered themselves an amateur - They often included sources and links - They were conspicuously respectful and humane - Meta-comments were productive, and typically stopped propagation of nastiness before it could take root
Often enough, comments would truly enrich the original post, and I was truly grateful for them.
This was a stark contrast with the subreddits that I frequented. (I gave up on reddit a few years when they changed the default format to be more attention-greedy.)
From what I've seen, HN has become increasingly noisy -- at times, it's angry -- but overall, it just feels loud and crowded.
For that reason, I've basically stopped reading comments at all, even if there is high-quality content in there. It is a damn shame.