The key difference is AI curation. What you see here depends on what time things get posted and how many up-votes posts get. FB, twitter, et al, decide what to show you based on what they think you will like using opaque complex software.

If a newspaper publishes a 'letter to the editor' that is libel they are liable because they chose it to publish. that's what the big tech social media do.

If section 230 got repealed it would have effects on sites like HN, but the would be catastrophic for big tech social media.