The endocrine system is very intricate and elaborate system. It complexity is significant compaired to the comparatively simple interactions of amphetamines, benzos, and opiates. It also is a entirely differentiated focus of study in science and medicine. Endocrinology and neurology. Many people who take one of the three you mentioned also take the others so knowledge and wisdom can be found grouping them with the others.
The drug world has also been really divided. So many groups look down on other groups and this keeps us divided. We are in a war here and divided and conquered is not anything we want to be a part of or promote.
What advantage do you see in splitting these users up?