It is the urge of others who apparently have some need to be giant busy-bodies in the lives of others to try to foist their opinions (which are often based on either nothing, inadequate/incomplete information, lies that come from someone's "agenda") on "everyone else" (or else on one or two "unfortunate beneficiaries" of the busy-body/know-it-all's ignorance and/or personality or ego flaw). Even when busy-body know-it-alls have some legitimacy to their opinion, they often (probably because they also lack human skills) lack the ability to sort out, reason out, and generally be non-dramatic ) - which so often means that what may have been a reasonably "legitimate" opinion gets twisted, mucked up, over-dramatized, exaggerated, etc. etc. to the point where (in the hands of a busy-body know-it-all) becomes a very flawed piece of "wind-baggery" (and presented by someone with an attitude that makes one partially feel bad for/partially want to "smash", and completely write-off as worth listening to/talking to).
Personally, I just can't imagine going through life aiming to mind the business of other people while also (as is most often the case) paying any attention to any of my own flaws/failings. These arrogant, aggressive (sometimes passive-aggressive), individuals just completely (as the question here asks) "perplex" me.
Well, maybe I should clarify... In some ways they don't "perplex" me at all. I have a pretty good idea about why they are the way they are and why they do and say the kind of stuff they do and say. No, the "perplex" part of my reply is more related to "What, on Earth, is like to BE one of these people?" One thing I do wonder about such people is whether they actually see/know the truth about what they do/say, or whether they can't/won't. Do they have short memories, lack of objectivity?
Do they consciously go seeking out situations that will allow them to fluff up their own sense of superiority, or is this behavior more a matter of ignorant, aggressive, inability to stop oneself? Were they helpless children who couldn't wait to grow up and "boss everyone else around"? Or, were they arrogant children who were never taught better than that?
Yes, to the extent that I ever have to think about/deal with these people, they do "perplex" me. They also disgust me, but no one asked about that. If they were smarter they'd know better. One just has to ignore them and/or put them in their place, right?