And you must not work in tech support. But all this is irrelevant for the most part because aside from understanding WHY it's useful and important, there's the fact that most people are using web clients, and trying to, say, sign or verify a message in GMail is pretty much an unclimbable mountain for the vast majority of people.

Heck, even on desktop clients it's a pain in the ass. Ever tried to create, install, and use an S/MIME certificate in a major desktop client, like Outlook or Apple Mail? It's ridiculous. An obscure mix of trying to use the right browser, export the certificate in the right format, sometimes even convert it on the command line, use the right mail client extension, etc.

So it's the tools that are the main problem.

Until S/MIME or similar is built into major webmail clients, and certificate creation and installation is simple on the desktop, it's never going to happen.