It's because of the history of racial discrimination in the US. While there's talk of affirmative action in the news, I suspect plain'ole racial discrimination is probably far more common.
To me that's exactly what helps lead to discrimination versus not knowing ethnicities and treating employees as anonymized numbers which would be fair to everyone.
Here is one example that might be interesting: https://www.npr.org/2024/04/11/1243713272/resume-bias-study-...