Because it doesn't imply that the treatment is successful. If I have a condition or disease it could be misdiagnosed as something much simpler and go unnoticed

Because it doesn't imply that the treatment is successful. If I have a condition or disease it could be misdiagnosed as something much simpler and go unnoticed by me for years. Maybe it's not debilitating but that doesn't mean it can't be cured or managed better. When/how do these errors get caught? I'm sure many never are.