I am a sewing educator, and have students from time to time ask me, why do you like doing this. I reply "I am a know-it-all who loves to be the center of attention, this is where I am happiest" haha
Granted that is really a joke, but I do enjoy being someone who has answers to their questions. I am not a know-it-all in the extreme, meaning, I am fully aware I don't know it all, or that my way of doing things isn't best for everyone (even tho I really think it is), that I will not get upset if they don't care for my techniques (which I am always learning new stuff myself).
There is some truth here tho. I grew up very insecure, unsure of myself. Being concidered an expert in this area, is an ego boost. I often DO have the answers they want, and when I don't, I know where to get them. I personally, don't feel superior, (I always say the definition of a teacher is "a person one chapter ahead in the book) but maybe some need to feel that. Their sense of self worth only comes from feeling like they are better or smarter than you.
There are some areas and interests I am very well versed in (as we all have interests we are passionate about and knowlegable in), and tend to speak up when I see something being misrepresented or whatever, but for me personally, it is not to "put them in their place" or prove something, it's usually just correcting the facts, not meant to be a put down at all. In the end, I really am a live and let live or believe or whatever kind of person, so I guess I am really not a know-it-all.
I just do honestly think there is an insecurity thing when someong is an in your face know-it-all about everything. I also find it sad, you can never really learn anything, if you already know "everything".
No idea really, just my 2 cents.