It disappeared because people disagree on whether to upvote or downvote comments. When the HN algorithm sees signals like comments receiving large numbers of up

It disappeared because people disagree on whether to upvote or downvote comments. When the HN algorithm sees signals like comments receiving large numbers of upvotes and downvotes simultaneously, it interprets that signal as "this post is controversial." HN explicitly and intentionally downranks algorithmically identified controversial topics in order to reduce the odds commenters behave badly (which is disproportionately more likely in controversial topics). The HN algorithm is intentional about a primary goal of driving well behaved discussions, even knowing that means important controversial topics getting downranked.