I'm gonna go on a stretch and argue that while it is true reddit/facebook/twitter killed these communities, I would argue it really had to do with the fact that

I'm gonna go on a stretch and argue that while it is true reddit/facebook/twitter killed these communities, I would argue it really had to do with the fact that: A: these communities never evolved with the times or tried to preserve it's relevancy to it's users - in other words don't touch if it ain't broke. B: Because of how insular the communities were - I think the admin always either assumed it was a small-time gig or that the community will stay together forever and ever C: These communities relied heavily on too specific fads (think Naruto fan sites or tumblr like quirk) - compared to start with a fad and then expand Essentially when you look at successful communities say Newgrounds and compare it with Ebaums World, you'll notice that Newgrounds while being slow it has always tried to stay relevant and branching out while Ebaums world just stayed the same never changing or adjusting and today all but a joke compared to it's former self. I think the fundamental flaw with (unchecked/nai cross-polination though is that while it is highly successful if done right, allowing unfeathered "all speech is free speech" MO that Twitter, reddit and even Facebook prided itself around 2010-2012 we know how poluted it can become with bad actors to the point it's a systemic problem / literally a threat to business model of said social media (for instance I know youtube's algorithm has been blamed for why extremist content garned such quick and effective attention).