I don't know the answer to this. I presume it's just the perspective some mental health professionals have. A different mental health professional might well have a different approach. I stumbled around the mental health care system where I live for around 20 years before I finally left if all behind. And I never got a diagnosis. In my case, though, I presume it had to do with my age. I think there comes a point in life where mental health professionals figure it's just too late to make it worth worrying about. I don't know... maybe they're right.