Huh, you signed up for Hubski the same day I did... What exactly did happen 649 days ago? I can't remember at this point :/
The problem is that as the good content becomes harder to find, the people who actually create that good content are less and less motivated to contribute. Thus you end up in a death spiral of memes and circlejerky injokes. Worse, a lot of the expertise is fake. Like, in the two games I'm playing right now I'm finding that the communities on Reddit that serve them end up being wrong more often than right. Finally, as the community overgrows its mechanics, visibility becomes ever more reliant on timing. Thus, you can say something insightful and relevant and be ignored while a not-great pun shoots to the top because more people saw it. Also, more people are under 15 and have no real appreciation for, you know, knowledge especially when it has to compete with fart jokes. And then you recognize that any time you say something useful about anything and it actually does get noticed, some bot is going to cross-post it to where trolls eagerly await the opportunity to make you regret contributing at all. It's been years since I've felt motivated to contribute to any subreddit ostensibly about any of my professional expertise. It's basically an excuse for a twelve-year-old kid to insult you and force you to explain standard terms while everyone calls you mean for using words they don't know.
I totally believe it. It's a systemic problem that outfits like /r/Askscience attempt to CSS away but then you end up with bullshit like the /r/politics posse arguing that Mother Jones is a spam hive. The basic problem is that Reddit was designed as a virulence engine and any attempt to tune it to community runs directly contrary to its core design. It's like trying to make a speedboat into a cargo hauler or a 747 into a pylon racer. Worse, from the top down they always institute the changes needed three years ago. I was talking about community stuff back before Reddit Gifts was a year old - top level shit. No one was interested. It would have been a double opt-in plugin that would have been invisible to anyone who didn't wanna play and there was straight crickets from the powers-that-be. Now? Now, in the year 2017, Reddit is discovering Facebook, long after everyone under 40 has given it up for Instagram and Snapchat.
You're backing into the truth despite bad data. Reddit's published numbers are between a factor of 10 and a factor of 100 off of what any other measurer uses. There are blog posts early on where the team slags on Alexa and the like because they aren't measuring "true" metrics. Those same rankers also point out the major terms that bring people to Reddit - and it's all porn. All of it. All porn. But reddit's numbers and reddit's monetization aren't inextricably linked because they bill you based on what they say the numbers are (and they rip you off HARD). However, they can't count when you have adblock on either, so yeah - it makes sense for them to serve the communities too stupid to run adblock. For the longest time, the only thing that gave you karma was outbound links. That's not by accident. Outbound links increase Reddit's siterank, internal content does not. Things flipped when 9gag and the like started raiding Reddit content; now you get points for pretty much everything you do... but it's still all about "what can we do to inflate the metrics." And yes. Nothing in /r/depthhub will do that. Imgur started out as a Reddit plugin. It now has higher profit and higher numbers. That's when Reddit decided to do their own image hosting - when they were basically an Imgur optimization engine. It's a shitshow from stem to stern.
I sorta think the VCs told Imgur to quietly add comments and become a community separate from Reddit because reddit is legit toxic. There's a reason they dont' get more money. Toxicity doesn't sell.