Forbes' Curtis Silver hits the nail on the head. TWTR's short character format and access to high visibility people/companies creates an environment for promotion of "zinger" comments that reach the top of the feeds and popularity/promotion outside the Twitterverse for a laugh or shock value at the expense of the target.
It also seems prevalent for users to lurk TWTR content that reaches outside sources without interacting with TWTR at all and merely giving a quick "like" with those outside sources when in agreement with the content... but it's not enough to drive them to TWTR because that's not where the discussion happens. TWTR is for saying things at people and it often takes anger for someone to actually create a TWTR account to voice their dissatisfaction with a game losing sports star, actor in a flop movie, jealousy of a pop star, politician backing unpopular views, a company cheating their customers, and so on. So for instance, it's very possible that the Q1 uptick in MAU's but flat growth in Q2 along with a drop of 2M USA users was simply a bunch of pissed off people who created accounts to give Trump the business but then gave up after they had their say and saw it wasn't really changing or getting them anything in return.
I honestly feel that YouTube has generally nicer and more supportive comments than TWTR with GOOG's greater resources to reduce toxicity. FB users simply have tighter control over their smaller circles of friends and opinions to sit more comfortably in their like-minded opinion bubbles by nature of the platform. So while I'll concede that TWTR's format still works well for providing the quickest bits of real time global happenings, it only alerts people that "something" is happening and then people go to TWTR's competitors to get the full mainstream media stories and opinions that side with their views. So TWTR's character limit means it's merely the messenger and has to step out of discussion where it loses engagement from there.
Unfortunately in pop culture, that message is often things like, "TWTR users thought Ed Sheeran sucked in GoT" and so he left TWTR and TWTR competitors benefited by serving ads to users reading and talking about it mostly everywhere but TWTR.
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