In my humble opinion, I do not believe that historians are neglecting the effects of disease on history, entirely. If they did then we would not know of many instances where diseases affected daily living during and after an outbreak. Therefore, one can posit the view that pandemics form a reasonable discourse from the historians.
However, I do believe that until a few decades ago, the style of researching history led many historians to pick the narrow field area for research. I realized that unless a disease was a specific case study, the historians focused on the subject’s relationship with other humans. A focus more on the political, social and even economic but sometimes the scientific explanation are missing. For example, let me bring up Louis and Clarke expedition, yes the political details of buying and exploration is readily available but it would take a specific case to draw a conclusion about Napoleon’s readiness to sell based on an outbreak of a disease.I am thinking it is because such discussion overlaps into Medicine and Science.
Is History a Science? is a question often ask (of old) when one tries to conceptualize the purpose of history and the methods use to arrive at a conclusion. Many historians left the scientific/medicine discourse for the scientists and doctors especially because of the debate of how far History could go/explain.Hence, in the 1950’s general history you will come across Cold War and Civil Rights but you may have to dig deeper for Jonas Sulk and the Polio Vaccine.
I believe it is with the growth of Medical/Medicine History, the historians in this particular field show disease as a phenomenon which influenced many societies. We now have medical journal database to learn about diseases throughout history.