Suicidality is an issue that's completely separate and apart. If somebody who is having suicidal thoughts goes in and sees a clinical professional and seeks assistance, that's somebody who is able to be helped.
Somebody who has a mental illness is somebody who, despite going and getting help for, potentially, decades, is unable to lift themselves out of that circumstance and is in an irremediable state, a state of decline, so there's an important distinction to be made.