While there are some mental health issues that are lifelong, many mental illnesses can be recovered from or at least greatly managed so that they don't impair quality of life.

I have been diagnosed with PTSD and bipolar disorder, both considered "lifelong," yet I am free from symptoms and have been for several years. Am I cured? Probably technically not; I'm more likely in what is considered remission. But these periods of years asymptomatic show me that these diagnoses are not "lifelong;" I consider them in at least partial remission. They are having absolutely no impact on my life at the present, have not for several years, and hopefully for years to come.

If I had cancer and went over 5 years without any recurrence, many doctors would declare me "cured." True, that doesn't mean there is a guarantee that there won't be a recurrence of the cancer; there is no way to be sure every cancer cell is gone, but the chances are much improved once a cancer patient gets past that 5 year mark.

Why can't those with mental illness fit that same criteria? Why does mental illness have to carry a "lifelong" sentence if the person is no longer impeded by the symptoms of said illness, particularly after a significant period of time without need for any form of treatment?