Even on reddit, when you get a high ranked comment, you will often get the same reply over and over again, even though a similar response is already the highest ranked reply to yours. There are people who just want to blurt out their opinion regardless of whether it's original or not..
I can't remember who I stole "the internet is write only" but it's felt very true as audience size exploded.
Perhaps the worst part is that it's self reinforcing in either direction, and few people ever leave the agora unless they delve into niche subjects, so they bring the agora mentality with them.
I think this is the key point. As with most issues on the internet, it's mostly an issue of scale. I assume these problematic users are actually only a very small fraction overall, but as the overall size grows, so does the number of people who belong at the very edge of the bell curve in terms of "normal" behavior.
With scale, any rare issue becomes common enough to be annoying.
"NB: if puzzled by a pawn move, please check for en passant before reporting a bug"