Common retort: don’t just downvote me, tell me why I’m wrong. I’m a professional who had signed off on legal documents. Why would the buck not stop at me? That’s the way it works in architecture and other professions.
I _think_ this rule is intended to discourage "Have an upvote" (and similar) comments, commonly seen on Reddit.
Reminding fellow readers/commenters to not just shallowly dismiss comments once in a while doesn't do much harm, and actually lead me to reply to the parent.
"Please don't comment about the voting on comments. It never does any good, and it makes boring reading." - https://news.ycombinator.com/newsguidelines.html