Everyone on HN exists in the same space. If you post something, a significant portion of users will see it. Most socials usually only show your content to people who opted into seeing it or otherwise came across it in a non-trivial way. With a click of a button you can auto-hide content you don't like.

A HN account doesn't have much value. Unless commenting on HN is what gives you joy in life, you won't be impacted much if you lose it. Major socials can be a big part of one's identity, the way one communicates with friends, work and businesses. The "value" of your account grows with usage. There's no chat on HN, no follower graphs or whatever. Pretty sure most HNers don't even notice usernames on here.

I do believe any business has the absolute right to censor anything they want. But in case of FB, Twitter etc too much censorship [0] compromises the value proposition. On HN it is the value proposition.

For the record, yes, I do think they're self sabotaging and will eventually pay the price. I'm guessing the demise will look much more like IBM rather than Myspace.

[0] For example, it makes perfect sense to ban people who actively harass others. Most users don't want to deal with too much nastiness, it reduces the value of your platform.