I always thought the whole prevention thing is because we want to “flatten the curve”, remember? Not to prevent every single infection, which is impossible.
As another fun example, the doctor (and only the doctor) overwintering in Antartica needs to have had their appendix out.
Medical evacuations are tricky, especially in the winter, and the logic is that the (single) doctor could remove someone else's appendix, but it would much harder for them to remove their own. Leonid Rogozov did remove his own in the 1960s, but I think most stations would prefer to avoid a repeat of that.
In the US there are literally thousands of different public health agencies headed by health officers with strategies ranging from herd immunity by any means necessary to attempting COVID 0. Vague gripes about public health tag lines in such a fractured environment is unproductive.
If you're on an Antarctic base where medical facilities are meager and the time and cost for evacuation is high, zero infections is likely the goal.
As an extreme example, the US grounded an astronaut for being exposed, not infected, by measles:
https://en.wikipedia.org/wiki/Ken_Mattingly#Apollo_13