> That's because calculus is taught in high schools and is generally taught in college regardless of whether you major in CS (so for example someone wanting to self-teach CS after college will have taken calculus).

The depth usually required for a CS degree is not usually required in high schools (and often not available there), nor is it usually a requirement for non-STEM degrees, and people wanting to self-teach CS after college will very often be non-STEM majors.