SEO with Google was about gaming PageRank. A lot of work happened in the 00s trying to prevent that, but it requires an army of moderators and others to identify good/bad links and link sources. Is HN a good source? Sure. Are HN comments a good source? Not once spammers realized they could drop links in comments to boost their site's results. How do you tell the difference? Plain PageRank is weak against this, and that's what motivated a lot of changes to the ranking system.