The mail server has to read the body of the mail message, which throws out any E2E use. SMTP is from the 1980s. There are countless SMTP servers on the Internet. You want spam filtering? Server-side rules? Can't have E2E.

That, and more, is why E2E isn't available for SMTP-based email. Many modern SMTP servers support opportunistic-TLS, potentially securing email traffic between two SMTP servers. Or forced TLS when you know the target supports TLS connections.

This isn't some "money making" or "spyware" conspiracy. It is a product of history, decentralization, and momentum.

Comparing that to modern chat apps which can be built from the ground up and their messaging protocol doesn't rely on a 40 year old standard is disingenuous at worst, ignorant at best.