It could be that these "this is not new" HN replies are not responding to the submission, its author or its subject matter but are instead focused on HN thread readers and other HN commenters and what those readers might think or how those commenters might react

If there is a submission or a comment that makes a claim such as "this is unprecedented", then a "this is not new" reply, preferably with supporting evidence, makes sense

But that's not what's going on here