How come no one who does their “own investigation” ends up agreeing with conventional wisdom?

Because, like that user who claimed that sharing what MIGHT have been Einstein's MBTI, he WAS Einstein, these ppl want attention and even to be looked on as savants...

But they often have little-to-no background in the area...and I've yet to see a savant doing that.

Investigation uses to clash with common sense.
But when "own" means to dismiss the work of the scientific community it also ends supporting conventional / religious worldviews.

Because
doesn't mean investigate. That would mean actually trying to understand the topic in question.

It just means
No understanding required, just a visceral reaction.