Chrome extension for end-to-end email encryption

So why doesn't this exist yet? Obviously Google wouldn't "like" it because then they couldn't mine our email for determining which ads to show us ... but presumably they wouldn't block such a thing, or would they?

It's striking that for web browsing this was taken care of (essentially) eons ago, but for email (a much older system) an "it just works" or "comes built-in" solution doesn't exist yet... at least not for the masses.