Question

why are latitudes and longitudes always expressed in angles

Answer 1

latitudes and longitudes are expressed in terms of degrees because degrees are parts of circles and lines running around the Earth are circles.

Answer 2

There are 360 degrees in a circle . longitude and latitudes expressed in this way because the earth is a sphere any line drawn around the earth ,then, is a circle ... Thus latitude and longitude are expressed in terms of degree because degrees are part of circles and the line running around are circle .