You can't teach people to do something less convenient than what they're already doing. Car keys are more convenient than never letting your car out of your sight outside of your own garage (which is what people were doing before car keys.)
PKI, as currently imagined, is less convenient than just speaking freely and feeling a nagging sensation that someone might be listening (which is what people are doing now.)
The difficulties in PKI are not that hard. Most of the problems are social, such as the belief that any implementation of PKI must be absolutely 100% bulletproof. Corporate deployments of PGP with no passphrase make the difficulty of executing spear phishing attacks considerably higher (especially when you consider that these are the usual way of getting initial access to corporate systems).
PKI, as currently imagined, is less convenient than just speaking freely and feeling a nagging sensation that someone might be listening (which is what people are doing now.)