Training In medical school, learning is likened to 'catching paint with a screen door'. This means that the information comes in faster than it can be assimilated. To compensate for the fear of not being competent enough, we often take on a reactionary attitude of infallibility. Along with this comes a belief that anything they didn't learn was not relevant. Therefore, any methods they were not exposed to could not have much merit.
Medical doctors are specialists in pharmacology and surgery.
The problem is that these specialists assume that their areas of expertise are the only ones relevant. Since they are not trained in areas of lifestyle management or botanical medicine, they don't realize the merits of other approaches. More evolved doctors realize their own limitations and don't castigate areas outside of their knowledge. Economics In America, medicines are patented. Much money is spent for approval studies, which is later recouped by tagging the cost of research onto the drug.