I think it keeps popping up because people are interested in investigating the impact of race as sociological construct on people's health outcomes.
It's a well-established fact that race is not a biophysical concept - as you point out, there is very little substantial genetic difference between races. That said, race is still a very real sociological construct, as recent events can well attest. People are treated differently by any number of different entities with very real power based on their perceived race. This can have all sorts of interesting impacts on their health. For example, Claude Steele has written elegantly on the role of "stereotype threat," and others have tied this into higher incidence of hypertension in African-Americans. I'm sure you know better than I do that genetics are just one component of the stew that determines who gets sick in what way - knowing what race people are (and whether it's self-identified, determined by an ADT clerk, etc etc) allows us to do interesting work describing the impact of being seen as X (and living in a society where people are seen as X are treated differently in Y ways). For example, some areas in Australia have implemented restrictions on gasoline designed to target inhalant abuse in aboriginal populations - knowing who is and isn't aboriginal affects our ability to assess the impact of this policy change.
I would frame it not so much as an insistence on racial differences as an insistence on the importance of being able to accurately asses the extent to and mechanisms by which structural racism creates and maintains the well-documented disparities in health between groups.