Perhaps the SAT does roughly correspond to IQ, but the reason to use IQ is to take into account unrealized potential in those who have had the misfortune of not being exposed to adequate education or of stimulating environments.
Admittedly, most people with intellectual ambition and special ability find a way to pursue it in youth, but there are surely plenty of diamonds in the rough out there with undiscovered glitter. If I were a college admissions officer, I'd want a kid with a 160 IQ and mediocre SATs over an over-achiever with decent SATs and a mediocre IQ.
Mind you, this is all about academic potential, not life potential. That's an entirely different topic. Only God can measure a life.