Top tier schools are a proxy for people who score high on SATs, and/or have wealthy networks that can get them in. Many of the companies that pay the most only recruit at specific schools for this very reason, the high hurdles of getting into the school itself give them candidates that have higher chances of being successful hires.

SAT is not a good indicator of success for a specific individual, but when sifting through thousands of people, it seemingly is a useful metric.