It's tradition at this point. Based on the upvotes the comment receives, it looks like many readers find value in it.

Upvotes are cheap, the fact that something is upvoted doesn't mean it's valuable (see: Reddit). Another thing is how insightful is the discussion under a typical pelican comment are (and how much of it is related to the pelican and how often it's just where the general discussion happens).

It could alternatively mean that many readers use Reddit. That doesn't mean that HN should turn into Reddit.