20+ years ago, in the golden age of internet forums when anyone could just sign up for a proboards or whatever, the key thing that kept a community growing was strong and fair moderation. The sites where clearly someone just wanted their own little community but had no desire to put the work in managing it dwindled quickly and died. Threads would just get spammed to death with none of it removed and it would be too hard to cut through the nonsense to bother.
This might well be what brings Twitter low, too. Nobody sensible is really interested in a communication platform full of rampaging bots and threatening replies, and once nobody is actually talking on Twitter any more and the bots & trolls find no joy in winding each other up, it'll be too late to salvage.
Maybe no single platform will become a true replacement in terms of size and each, and the internet's chat areas will fragment back a little. Perhaps that's not a bad thing.
