Lesson from the Climate Email Hack

Why isn't email encryption more common? I suppose in that case the email was probably stolen from the server, so soft-core encryption (encrypting the email when transmitted outside the trusted domain) wouldn't have prevented it. That would have required hard-core encryption--where the message is only decrypted on the client computer, viewing the email. And most people think of soft-core encryption when they think of email encryption. Still, it is surprising to me that it hasn't taken hold, at all.