It's not a reproach at all! We do this all the time when something has appeared before on HN, so that people can look at older threads if they're interested. It's significant signal that a particular post has appeared repeatedly on HN over the nearly two decades we've existed. It's also interesting to see how the style of discussion about the topic may have changed over time.
It's already a feature (click the link domain).
That isn't always a simple, reliable way of finding the historical submissions of the article. Sometimes it's on a domain that has had many other submissions. Sometimes the domain has changed or the content appears in different forms in different places.
It's a longstanding convention to do this, and the audience appreciates it. Not sure why anyone would take issue with it.
It does appear a bit mechanical, like something the system would do. Maybe a submission should always automatically find all previous discussions as an automatic comment.
It's not a reproach, there are no negative words in the comment.
It's a gathering of information so that people can get more comments.