While high school courses are not the same as college courses, the material taught in high school courses for advanced high school students may be the same as that taught in frosh-level college courses for less advanced students. Of course, whether the college accepts AP or IB scores for subject credit varies, depending on the specific course and college. But when the material is the same, there is no reason to require an entering college student who (for example) had calculus in high school and did well enough by the college’s satisfaction to have to repeat the same calculus after entering college, rather than moving on to the next more advanced math course.