I think the problem is misalignment of incentives. If I'm incentivized to increase engagement, then I can think of some pretty ridiculous shit to say that will get lots of people clicking downvote and shouting at me.
I think these platforms could have been more proactive in setting those cultural norms that evolve into fruitful social interaction.
You will see a lot of toxicity and you can find several deleted or heavily downvoted comments.
As even HN front page and commenr section is algorithmic. Vote brigading happens here as well for posts and comments.
I personally like that they try to play down controversies instead of optimizing for engagement from them.
Imagine a big social media platform doing it. Just because some topic became a flamewar if it gets removed, one party will blow it up as them being censored. When these posts are started by your ruling lawmakers, it can even be cited as contempt. It is an extremely tricky thing for big social media platforms to moderate content.
Thousands of years of tribalistic evolution can't be removed in just a few decades, this is a lot on how humans interact.