On the margins, SATs are a "fairer", harder to game metric than most of the others.

Yes, rich people can put their children through test prep courses. However, the differential impact is much less than what they can do with grades or even worse, extra-curriculars.

A bright, economically disadvantaged teen can do very well on a standardized test. That same teen has no way of doing an impressive non-profit over the summer in another country, as many wealthier Ivy League applicants do.