I have no science to back up my claim but my knee jerk hunch is that people who weren't supported by their peers during the learning process go on to develop imposter syndrome.

Y'know like the classic story of being outcast unless you hide being into learning "You read books?! What a nerd!", "Teacher's pet!", "Why don't you go invent a gravity, Einstein"

Without early peer support there's no foundational confidence in your abilities and without that comes imposter syndrome later

Again I have no data other than my own experience, n=1 and barely at that. You'd definitely want to ask around a bit to see if this even matches up with other peoples experiences before accepting it as any sort of truth

E: It might not be that specific, any sort of educational trauma (for lack of a better way to describe it. Learning disorders, dyslexia, a lack of school experience entirely, having to take care of someone during your school years) would probably do it if the foundational skill confidence theory is in any way plausible