Where do they do that? Even the notorious punching bag of Affirmative Action is intended to make up for prior bias, not force equal outcomes regardless of all merit. (Whether it actually does that is another question, but "try to enforce" is all about intent.)

Let's start with this NYTimes report about allegations of bias on teacher's qualification tests, because of the disparity in results:

http://www.nytimes.com/2015/04/08/nyregion/questions-of-bias...

You probably assume that the test is unbiased unless proven otherwise, and that any discrepancy is therefore likely to be actual differences in the underlying populations. The court is merely assuming the opposite: that discrepancies in the test results are a result of bias in the test itself unless proven otherwise.

They aren't trying to force equal outcomes, they're trying to make sure that if a test produces worse results for minorities then it had better be because of actual differences in the population and not subtle bias in the test.