They've been using academic success to predict career success. I agree it's a good predictor. It's not foolproof though. The issue is that it can be skewed by devoting more resources to academic success instead of for example starting a business or political action or sports. Is someone less likely to have a successful career because they started a business instead of studying an extra hour every day? This is why the most elite schools switched to extracurricular and interview heavy admission criteria which ended up disfavoring asians who tend to spend more time on academic success.

The goal was to actually do a better job of finding the applicants with discipline and grit, not just the ones who have it in an academic context.