Many users turn to "encrypted" email services that promise to safeguard their privacy through means that cannot be easily verified, such as robust encryption in transit and at rest, secure server facilities in World War II bunkers and privacy-oriented legal jurisdictions. While it's unnecessary to mention specific providers here, what they all share is that they profit on the general public's lack of knowledge about email systems.
The privacy assertions put forth by these service providers are probably partly valid in a very particular circumstance: when messages are shared between two users operating within the same closed system. However, it's imperative to underscore that these closed, internal exchanges do not represent email systems. Email is fundamentally designed for open systems, not isolated internal ones.
Roughly 80-90% of global email is managed by either Microsoft or Google. Even if someone opts for an exceptionally privacy-friendly messaging service, there's a 99% likelihood that their counterpart is using one of these major companies' services. This begs the question: what value does local privacy provide when copies of most of our messages are readily available to the largest data-mining entities that collaborate extensively with governments worldwide?