What is the job role of a biomedical engineer and why is it not directly mentioned just like mechanical electrical, etc engineers?

The role of biomedical engineer is the speciality in medical equipment maintenance and manufacturing. yeah you are right that it is not mentioned as other engineers. one of the reason is, job role for this discipline is less as compare to others.

A biomedical engineer is specialized in medical instrumentation including everything from small measurement and phyisiolgical signal acquisition devices to large radiography, imaging and nuclear medicine machinery. This specilaization provides the biomedical engineer with a broader knowledge and comprehension of the requirements that accompany this field. A large part of this knowledge relies on the understanding of the medical aspect and demands of these devices. While a mechanical or electrical engineer might be qualified to set up such instrumentation, they might face difficulties in the overlap between engineering and medicine. 

BIOMEDICAL ENGINEERING IS THE ART OF SCIENCE WITH MACHINES THAT ARE LIFE SAVING ANDD PROTECTING

Biomedical engineer is the speciality in medical equipment maintenance and manufacturing. yes, it is not mentioned as other engineers. one of the reason is, job role for this discipline is Incorporated with Electrical,mechanical engineering and its less as compare to others.