The problem with email encryption is not about CAs or verification of keys at all. The problem is key management and how encryption interferes with the common expectations that users have about email. In a corporate environment it is easier because the corporation itself can manage user keys and issue yubikeys etc., but for individual users there is no such support. It is also clunky to have to first receive someone's public key before you can send an encrypted message; for chat apps that is not a problem because chat is interactive and typically real-time, but with email there is no guarantee about interaction.

Those issues are partially addressed with "identity based encryption," but IBE always has a "backdoor" because there is a party that issues the users' private keys (and hence can always read a users' messages). On the other hand IBE does allow you to "just send" an email to someone because the public keys are just the "identities" (e.g. email addresses) combined with a single master public key. Key management is not as much of a problem because of how keys are generated. IBE does have some users, but as you said it is mostly business/organizational use.