It's just for fun and interest, as the other replies have pointed out. I've added my standard disclaimer to the comment above. Reposts are fine after a year or so! This is in the FAQ: https://news.ycombinator.com/newsfaq.html.

Thank you for the link to the FAQ! Unless I blacked it out, I don't think I have read it before. Now that I know it exists I can see it clearly in the page footer, alongside the Guidelines... I will go and read those, but I also wonder if this should be reposted from time to time too.

It's so that people can see the previous discussion if interested. 'about once a year' does happen to be the frequency at which reposts don't count as dupes on HN but that's somewhat incidental.

dang (the moderator of hn) does this for many/most common reposts. It is done without comment or implications.

For what it’s worth I check the site fairly frequently and this is my first time seeing this. It would be interesting if there was a way to mark links as seen so they could be removed from your feed in the future for people who don’t care for reposts.