Because normal people do it know what a “signed email” might mean. Also, both PGP and S/MIME are hot messes of insecure 1990s cryptography with no reliable key

Because normal people do it know what a “signed email” might mean. Also, both PGP and S/MIME are hot messes of insecure 1990s cryptography with no reliable key distribution, no authenticated encryption, and meaningful headers which are not covered by the signature.