Your operating system and half the software you use has integrated spyware that can read anything you see on your computer or phone as free text and use that information to notify state actors or just whoever the fuck they want of the contents. It doesn’t matter that the message was encrypted between you and the other person when they can spy directly on your device.

Its like passing a coded note to a friend in class and then they open it and just read it out loud to everyone sitting there. Didn’t really matter that you encoded it.