That critical mass may be online now. And the internet is so silo'd that it may not form or may not be noticed.
i.e. readers will only care to remember the most notable/unique/etc... fraction of comments.
And everything else will just meld together into one big mental blob.
Maybe that is why there's been a flight to smaller online communities?, even 'Joe Average' has realistic prospects of writing something memorable if there's only a few hundred folks to compare against.