Why aren projections with less distortion used?
Most of these maps use a rectangular or Plate Carre projection because it is trivial to project latitude and longitude into map coordinates. The polar maps are a special case for paths that traverse the Arctic (or Antarctic) regions of the globe; with the restricted set of maps the orthographic projection didn’t require much additional work to implement. Together, the results are adequate for the intended purpose, so I didn’t want to invest a lot of effort (and compute time!) on more complex projections.
