The reason for that is HN is not for direct profit, has a charter, is not afraid to moderate content, via flag, and to bar people, via marking them as dead, and

The reason for that is HN is not for direct profit, has a charter, is not afraid to moderate content, via flag, and to bar people, via marking them as dead, and actively hunts spam and trolls. If Twitter/FB were to do this, they'll have 1/5th the customer base but will have more sane content.