which of the following is not a reason why communicable diseases, such as pneumonia, kill fewer people today than they did in the past?

The reason that is NOT why communicable diseases, such as pneumonia, kill fewer people today than they did in the past is "slower population growth." This factor does not directly impact the spread or treatment of communicable diseases. The actual reasons include continuing medical advances, improved living conditions, and better preventive treatment, all of which have contributed to the decline in deaths from such diseases over time.