Lawsuits and Affirmative Action.

Companies are generally trying to avoid lawsuits. If they  are openly not hiring incompetent people, then they are guaranteed to get lawsuits piled onto them. So they have to make  a show of being interested in hiring  people that got their degree because of Affirmative Action. 
But then they need to have competent people to do the actual work, so they have to hire only whites or Asians.