Why does the quality of a news site like slashdot, digg, reddit, or Hacker News deteriorate until it reaches annoying levels? Because if it didn't, then more and more people would join, reducing the average quality of the participant pool.
which is a good thing considering by the time that happens to reddit, kn0thing will have made his impact, and will be able to do whatever else he wants, and somebody else's site will be the new and popular one (until it is).
The only thing that Reddit has going for it is that has a way to build new communities built in. /r/DepthHub, /r/math, and /r/askscience are doing just fine.
The "only" think Reddit has is an engine to sustainably produce new communities as good as the original Reddit, at the cost of providing a pile of chaff I dislike that thousands of people enjoy?
Perhaps an astrophysicist will one day explain why communities like Reddit tend to implode.
Once the "pressure" of those in the core, which are the ones doing most of the work to keep people in line and promote healthy community behavior, start to fizzle out and aren't replaced, the core will implode and the whole thing will go supernova.
Smaller communities, like smaller stars, seem to have much longer lifespans.
The good news is when a site like Digg or Reddit goes supernova it spreads a lot of well-intentioned people around the greater internet to create their own new communities and start the process all over again.