I think people can now see how ridiculous this is for the most part - which is why the revisionists and their ilk don't use the same techniques anymore - but at the time it was really believed that a person's physiognomy was determined by his character (or vice versa). And such a belief was popular for so long because it was in keeping with what people want to believe on a subconscious level. And the sad thing is, even if we've moved beyond judging people's characters by their appearance on an intellectual level as a society, we certainly haven't on that subconscious level, which is why these myths can perpetuate in less obvious forms.