There is a Supreme Court ruling that IQ tests are assumed to unfairly disadvantage minority candidates. This was in the context of employment rather than college admissions, but I don't think anyone has been bold enough to test whether it applies.

Broadly speaking, IQ tests tend to include a lot of cultural assumptions and therefore members of the in-group will test higher than members of out-groups of the same aptitude. IQ tests are therefore treated as discriminatory (disproportionate impact) "by default." The administration of a particular test for a specific purpose can usually be OK'd by either showing that particular test is not discriminatory, or by showing that particular test has a measurable correlation to the specific purpose for which it's used. My understanding is that "specific purpose" in the employment context means the individual job description, not just hiring in general.

SAT presumably tests you have learned certain things in high school and so are ready for university. E.g. you won’t show up to your first university math class needing to learn all of high school math, and thus be unable to complete the class.