What has been the main cause of the dichotomy in the way physical and mental health issues have traditionally been addressed by the health care delivery system?

Answer 1

It starts with general theory both medical and psychological. Theories are derived and different people are drawn to different ones (typically ones they can relate to on a personal level) and the immerse themselves in it trying to learn everything they can. Education comes into play and different schools and different educators within those schools teach what they have derived from their studies. This shapes a students direction in each field and what theory or theories they feel are right/best. Then they practice this way. There has been little effort for people to consider the big picture and integrating both mental and physical health when treating someone. It's not cost effective for the practitioner, it's time consuming and most likely one or many aspects of either will go against their own personal methods of practice. Spend time working in a hospital and you will see how not only do different medical units fight one another forget about different areas of practice. The "it's not my job" is it's own disease.