Hmm... maybe because these notable angles are also those of which the associated trigonometric values are round(ish), and so it's about first learning those by

Hmm... maybe because these notable angles are also those of which the associated trigonometric values are round(ish), and so it's about first learning those by heart ? (Like you learn the multiplication table by heart before doing multi-digit multiplications.) https://en.m.wikipedia.org/wiki/File:Unit_circle_angles_color.svg https://en.m.wikipedia.org/wiki/File:Unit_circle_angles_colo...