They switched their best sorting algorithm to be engagement based rather than upvote based [1]. Upvotes are just one of many metrics, but heavy comment interaction is another. It incentivizes rage bait and performing for the crowd with every comment and post. They also switched into an almost purely moderator curated frontpage [2] rather than allowing users to vote.

1: https://www.reddit.com/r/blog/comments/o5tjcn/evolving_the_b...

2: https://news.ycombinator.com/item?id=36040282

One of most magical things about HN is that heavy comments are punished as a negative signal, not rewarded as a positive one.