Test scores.
In order to successfully sue someone for $5 million you have to prove that you've suffered damages in the amount of $5 million.
How does someone prove that their failure to get admitted to Yale has cost them $5 million? Yale can produce plenty of evidence to show that many of their enrolled freshman don't graduate because they drop out, fail out, and occasionally even get arrested and go to prison. And even those who do graduate don't ALL get highly-paid jobs.
Something else to remember here is that nobody who is applying to a college (especially a private one) has a legal claim on a seat in a college. Depriving someone of admission to a school doesn't take something away from him that he OWNS ... so a major hurdle here in these lawsuits is that a plaintiff is first going to have to demonstrate that he even has the legal standing to file the suit in the first place.
they simply do not want middle-class white kids.