I found a post from a few years ago detailing just what percentage of reddit users actually post anything:

• Askreddit has about 15m uniques, and 500,000 unique commenters.

• /r/pics and /r/funny have about 10m uniques, 200k commenters

• /r/TIL and /r/videos don't have public traffic stats, but have about 150k unique commenters. nor do /r/pcmasterrace, /r/wtf, /r/gaming, all with around 120k commenters.

• The following all have about 100k unique commenters and the following uniques: /r/leagueoflegends 8m, /r/worldnews 6m, /r/news 6m, /r/movies 5m, /r/adviceanimals 3m, /r/gifs stats not public.

Conclusion:

The largest subs see from 1% to 3% of uniques comment per month.

So Reddit consists of 97-99% of users rarely contributing to the discussion, just passively consuming the content generated by the other 1-3%. This is a pretty consistent trend in Internet communities and is known as the 1% rule.

But there's more, because not all the users who post do so with the same frequency. The 1% rule is of course just another way of saying that the distribution of contributions follows a Power Law Distribution, which means that the level of inequality gets more drastic as you look at smaller subsets of users. From this 2006 article:

Inequalities are also found on Wikipedia, where more than 99% of users are lurkers. According to Wikipedia's "about" page, it has only 68,000 active contributors, which is 0.2% of the 32 million unique visitors it has in the U.S. alone.

Wikipedia's most active 1,000 people — 0.003% of its users — contribute about two-thirds of the site's edits. Wikipedia is thus even more skewed than blogs, with a 99.8–0.2–0.003 rule.

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Participation inequality exists in many places on the web. A quick glance at Amazon.com, for example, showed that the site had sold thousands of copies of a book that had only 12 reviews, meaning that less than 1% of customers contribute reviews.

Furthermore, at the time I wrote this, 167,113 of Amazon’s book reviews were contributed by just a few "top-100" reviewers; the most prolific reviewer had written 12,423 reviews. How anybody can write that many reviews — let alone read that many books — is beyond me, but it's a classic example of participation inequality.

I don't know how that author identified the most prolific reviewer at the time but I found one reviewer with 20.8k reviews since 2011. That's just under 3,000 reviews per year, which comes out to around 8 per day. This man has written an average of 8 reviews on Amazon per day, all of the ones I see about books, every day for seven years. I thought it might be some bot account writing fake reviews in exchange for money, but if it is then it's a really good bot because Grady Harp is a real person whose job matches that account's description. And my skimming of some reviews looked like they were all relevant to the book, and he has the "verified purchase" tag on all of them, which also means he's probably actually reading them.

The only explanation for this behavior is that he is insane. I mean, normal people don't do that. We read maybe 20 books a year, tops, and we probably don't write reviews on Amazon for all of them. There has to be something wrong with this guy.

So it goes with other websites. One of Wikipedia's power users, Justin Knapp, had been submitting an average of 385 edits per day since signing up in 2005 as of 2012. Assuming he doesn't sleep or eat or anything else (currently my favored prediction), that's still one edit every four minutes. He hasn't slowed down either; he hit his one millionth edit after seven years of editing and is nearing his two millionth now at 13 years. This man has been editing a Wikipedia article every four minutes for 13 years. He is insane, and he has had a huge impact on what you and I read every day when we need more information about literally anything. And there are more like him; there is one user with 2.7 million edits and many others with more than one million. Note that some of them joined later than Knapp and therefore might have higher rates of edits, but I don't feel like computing it.

Twitch streamer Tyler Blevins (Ninja) films himself playing video games for people to watch for 12 hours per day:

The schedule is: 9:30 is when I start in the morning and then I play until 4, so that’s like six, six-and-a-half hours,” Blevins said. “Then I’ll take a nice three- to four-hour break with the wife, the dogs or family — we have like family nights, too — and then come back on around 7 o’clock central until like 2, 3 in the morning. The minimum is 12 hours a day, and then I’ll sleep for less than six or seven hours.”

And he's been more or less doing that since 2011, even though he only started bringing in big bucks recently.

He's less prominent now, but YouTube power-user Justin Y. had a top comment on pretty much every video you clicked on for like a year. He says he spends 1-3 hours per day commenting on YouTube, finds videos by looking at the statistics section of the site to see which are spiking in popularity, and comments on a lot of videos without watching them. Maybe he's not quite insane, but he's clearly interacting the site in a way that's different than most people, essentially optimizing for comment likes.

If you read reviews on Amazon, you're mostly reading reviews written by people like Grady Harp. If you read Wikipedia, you're mostly reading articles written by people like Justin Knapp. If you watch Twitch streamers, you're mostly watching people like Tyler Blevins. And if you read YouTube comments, you're mostly reading comments written by people like Justin Young. If you consume any content on the Internet, you're mostly consuming content created by people who for some reason spend most of their time and energy creating content on the Internet. And those people clearly differ from the general population in important ways.

I don't really know what to do with this observation except to note that it seems like it's worth keeping in mind when using the Internet.

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Edit: I guess my tone-projection is off. A lot of people seem to be put-off by my usage of the word "insane." I intended that as tongue-in-cheek and did not mean to imply that any of them literally have diagnosable mental illnesses. I have a lot of respect for all of the individuals I listed and they seem like nice people, I was just trying to make a point about how unusual their behavior is.