There are many better communication systems.

To know your messages are meant for you by the person who claims to have sent them, it's really good to be able to keep a private key that is actually private.  This is hard for me to do.

What device I'm on switches.  Right now my device is an android phone that runs very very slowly and often misbehaves.  A private key kept on this phone, which sometimes does things on its own while I am looking at it, and sometimes may wait a few minutes to respond to touching a button, would make security more complex.  I would barely have confidence that the private key was private, because I don't know how to make the phone behave reliably.