Obviously, not all people vote or comment either so that's a second multiplicative factor.
Finally, causation != correlation, which most likely is your point, e.g. things on HN already spread from somewhere else.
[0] https://en.wikipedia.org/wiki/1%25_rule_(Internet_culture)
HN is brutal when it comes to comments, not as harsh as StackOverflow, but the probabilities of a comment being received well here are so low. To me, the expectations generally seem to be that: individuals are discussing in good faith, the comment is not “booby trapped” to intentionally cause a negative emotional response, the poster has taken some non-negligible amount of time to form their thought or they are clearly versed in the topic (ie use the correct lingo, etc), any tinge of a political perspective leans libertarian, etc. Those are some of the factors I use to judge whether I should post a comment on HN.
On Reddit, the filter is “is my thought hilarious” or “I can significantly improve the direction of this conversation by participating.” On StackOverflow, my filter is, “has any other human that’s ever used SO ever wondered what I’m about to ask?”
> stating that only 1% of the users of a website add content, while the other 99% of the participants only lurk
Currently there's a topic on the front page discussing this in detail titled - 'Most of what you read on the internet is written by insane people' - https://news.ycombinator.com/item?id=25600274
[1]https://en.wikipedia.org/wiki/1%25_rule_(Internet_culture)