Yes, some of them have been banned, and sometimes the reasons for those bans are dubious because Twitter does not consistently enforce their policies. But that is a separate issue from what's under discussion here.
Then 'real' users who started typing would autofill with the false one and the topic would lose steam quicker. Of course, without knowing Twitters proprietary algorithms, this is all just anecdotal.
To me it seems like two different cases that are easy to distinguish.
> Eschew flamebait. Don't introduce flamewar topics unless you have something genuinely new to say. Avoid unrelated controversies and generic tangents.
Call of Duty, Wolfenstein, Battlefield 1942 if I recall correctly; were all anti-Nazi and it was basically it's own genre of first person shooters.
Then everything moved towards terrorism related themes (Counterstrike starting that I'm guessing)... then political correctness just referred to it as "Opposing Force (OpFor)".
Weird times we live in.
At the same time, they have not done anything to reduce certain types of spam, such as the repeated reply chains under the President's tweets, which can so easily be identified as spam by the fact that they are unrelated to the parent, and appear in the same order under a number of parent tweets.
It's a total mess.
Added: I went back to find an example of the spam chains to reply to Srslyjosh, but I'm pleasantly surprised that they seem to have finally eliminated them. I withdraw that specific criticism I guess.