I like both points here. Twitter gets traction because professional trolls / grifters use it to build their personal brand.
They are frequently newspaper columnists, authors, and TV pundits who benefit directly or indirectly from have a large number of followers (whether they following in agreement or follow out of outrage, it matters not).
Sadly this is true of the left as well as the right; they are all selling something.
These Professionals need large mainstream audiences, which is why they love twitter and twitter loves them, but they are a different animal to the tribalists who want to satisfy their need to mix with like minded people.
Until the fringe sites enable the former as well as the latter it's not immediately obvious how they remain viable.