The US federal government doesn't proactively start asking such questions of employers. They only act on potential civil rights violations in response to a credible formal complaint.
Thanks for clarifying, makes sense. Ultimately that demographic data gathered from employees helps the federal government with legitimizing those formal complaints, acting as potential supporting evidence.
Tl;dr: it is less about the company being less racist on their own by knowing the race, it is more about the company having to report those numbers so that others could hold them accountable (in case there are any arising concerns about racism).