Could have been better

Can anyone explain to me, why there’s a trend amongst all the mail apps developers of simply not implementing a “no message preview” feature? I don’t understand why this simple, by default option is not in the app of the biggest IT company which trades on the sharemarket. It’s a simple feature that allows me to see who sent me the message, it’s subject, but not the whole message!!! And most of all, I don’t want anyone to see this message on the lock screen...

Sergey Zametalin about Gmail - Email by Google, v5.0.171217