plane geometry and spherical geometry are both overly simplified estimations of reality which appeal to people's imagination because they make the mathematics involved easier to understand. the people who are at the top tier of cartography that influences and controls the imagination of everyone else, aren't good at math.
fortunately for them there are a zillion convenient trigonometric relationships in imaginary euclidian plane geometry that have already been figured out by previous generations and pass down the eons. 400 years ago the wizard marvelous merchiston translated most of those relationships into spherical geometry and those are the limits of mathematical ability for contemporary cartographers.
if the earth is a shape other than a perfectly flat plane or a perfectly circular ball then the top echelon of map making will never realize it because an imperfect shape is outside of their thinking ability.