As I understand it, Trolls, typically - present extreme views which don't seem sincere about on reflection when you think about what they said - and the way they respond is unlike just about anyone else in similar situations, and somewhat incoherent on reflection.
find ways to bring in one extreme topic after another in a single conversation (usually by using examples or by remarks about others in the conversation) until they find one that "scores".
comes over as rather incoherent because they aren't really trying to put forward a coherent position or view. Just churning out somewhat coherent rambling thoughts as they try to hit a sore spot in the listener.
Use words that hurt, but don't lose their temper as they do so - because they are often not interested in the topic anyway, it's just an amusing game to them, seeing which buttons they can press. The words are often incongruous with the tone of the rest of their conversation, a few words of extreme violence suddenly in an otherwise calm conversation.
Are very likely to introduce certain key topics (nazis of course famously, but many other such) into conversations that are nothing to do with these subjects. Often you can't understand what the connection is between these topics and the rest of their post. Again, as just one sentence in an otherwise normal seeming post quite often.
It is very unlike normal conversation in how it works.
Trolls as I understand it, foremost characteristic, not sincere, just playing a game with words which amuses them.
This works fine on forums as a way to get people worked up which is their objective. But a trollish answer is typically
Rambling
Incoherent, with sudden switches of topic in a single post
Doesn't present any particular perspective or point of view - they keep switching their views until they find something that scores.
Brings in examples that are not relevant to the question
Inappropriate in tone to the conversation
Seems pointless to most readers
It would just get downvoted or ignored or reported as not answering the question and hidden.
The skills trolls develop through long experience of internet trolling simply are not very useful when it comes to writing coherent and useful answers.
So they have to take off their "troll hat" if they are trolls.
Can happen in conversations in the comments. But quora lets you delete any comments on your own answer. So trolls would know that. And anyway the way it is laid out the comments aren't immediately obvious and when you go to them, a trollish thread would be only one of several, and would be downvoted and eventually hidden or reported.
So all of that is not likely to bring trolls the amusement they so crave.
Just a hypothesis and thoughts but I think this might be the reason. In the topics that interest me I'm yet to see any example of successful trolling on Quora. I've had a few heated conversations where people have strong views. But nothing I'd call trolling, nothing where you feel the other person is insincere, just trying to hit sore spots to make people angry for amusement.
It's somewhat the same on facebook because trolls know they can be blocked easily or removed from your friends list, but I have been trolled on facebook, once, by someone who admitted he was just trolling when questioned. I could easily have unfriended him but when he admitted trolling didn't need to. Just said I don't permit trolling on my own timeline because I feel it is a waste of everyone's time, and that was the end of it.
I think quora seems particularly "not troll friendly" in the sense that - not that they can't come here, or even that they can't post troll answers (I have seen a couple of answers that read as if probably posted by trolls attempting to troll) but they find troll behaviour just doesn't work here. It just gets downvoted and ignored, the very thing that trolls hate happen to their comments. So you don't need even to unfriend them or block them, at least I've never had to yet.
I wonder, maybe it can help trolls become non trolls or at least develop more non trollish interests??
Quora User (sometime volunteer, non company, quora admin) says in a comment on this answer that quora has a trolling problem in questions, not answers.
Which he says is the reason for the Quora policy about Needs Attention
They are trying to get people worked up, and get amusement from the lengthy answers quorans sometimes write for obvious questions.