Personally I think to an extent we are still dealing with the by products of outdated and largely pseudo scientific psychiatric diagnostics which has always tended towards classification based on symptoms rather than an understanding of underlying aetiology. With the advent of trauma informed diagnostics, and a more subtle understanding of the complex interaction between developmental and genetic factors that is beginning to change but the change is slow and there's lots of inertia. In the old system symptoms become elevated to the level of illnesses; for example anxiety and depression are both symptoms, to elevate them to conditions in themselves is rather like calling an illness 'pain disorder' - as with the symptom of pain, anxiety and depression (and many other mental health symptoms) reflect underlying issues that on a deeper level may well be seen as a unified whole, rather than a separate collection of disease entities. While occasionally it may be valid to erect a disease entity of say 'chronic pain' in reality that sort of symptom level construct indicates that the underlying causes of that pain are largely unknown, once the causes are known they would be the more appropriate diagnosis (eg chronic pain as a result of fibromyalgia, or arthritis etc).