“Everyone” may be overly broad… just about everybody with any technical inclination knows yes, but for many years now the overwhelming majority of smartphone users have not been particularly technically inclined, and as such I would not expect most of them to be aware of the security and privacy implications that come with use of the various messaging services.
With that in mind, I’d say that most messaging apps don’t go far enough to make that distinction clear. Any app handling SMS or any other unencrypted messages should have ever-present, readily visible warnings when conversations aren’t encrypted.