Yes, Mac developers tended to focus only on that platform, and a large portion of its user base was on monochrome for a long time. Therefore, you had a sizeable group of artists and devs who got developed strong techniques for monochrome art.

Comparatively, on PC I never saw CGA graphics which I didn't think were anything but compromised EGA images, which were themselves degraded from VGA images etc. Did anyone else play Prince of Persia on a CGA display?