Flags are from users. So to some extent it's random personal opinion and unless you identified all individuals who flagged it and asked them why?, you aren't going to actually know, though it is fairly common for someone to give their opinion about why they think it was likely flagged (and sometimes I appreciate their observations and sometimes I'm kind of like "That's just your opinion, man!").
My finger was hovering over the flag button for a while. I was following the discussion and for the first hour or so the comments were of ridiculously low quality. I think of the first 20 comments less than 5 had positive score. I was thinking of flagging it because I just didn't see how any good discussion could form on it. I didn't flag because it seemed like the post itself had relevance.
It's rare for me to flag something. I usually try to leave a good faith comment if it seems worth discussing and the initial comments are sucky.
I'm not saying that's some kind of "right" way to handle it. That's just how I behave -- or try to behave -- and there are myriad factors that influence those choices. I'm just talking here.
