The "tiny" difference is, I guess, that among general population (almost anywhere) you have people of all ages... from newborns to those older than 100 years. Some of them will, certainly, fall sick at some point. On the contrary, people who are part of expeditions to such remote locations such are South Pole station or other stations "down there" must be checked as well as astronauts to reduce the risk of health problems to the absolute minimum because any evacuation (or delivery of medical supplies for the particular problem) would cost tens (in some causes hundreds) of thousands of dollars. Number of serious health issues occurring probably doesn't justify having a large and well equipped medical facility.
Note: I have never been there, but this is just my guess based on the research. I wish I am wrong but I guess I am not