Tony the tiger says "that's grrrrreat." Now, send an e2e encrypted to another email that is not yours and see how long it takes them to understand what you sent. PGP for email has been around for a very long time, and there's a reason it is unheard of by the general public. it is a pain in the ass.
S/MIME on the other hand is supported by majority of common email clients. PGP sucks in other (cryptographic) ways as well.
What's difficult is long-term key management. This is being solved in the context of Passkeys and the same infrastructure could be used for S/MIME keys.
Provisioning should become significantly easier with ACME for S/MIME, we'll see about that though.
Nothing really says it has to be difficult, even for the layperson.
Or, it's just too good. Why did it take so long to have encrypted DNS? Another example, https, which uses tls for secure communication still manages to leak the domain name because the Server Name Indication in the ClientHello is sent in plain text before encryption is established. The solution, ECH, is no where to be seen.
The folks that read your e-mail and monitor your online presence do not want you to use these tools.
