Interracial dating issues

I never understood people who have an issue with interracial babies and relationships. I’m at the WIC office, and I just witnessed a black man/white woman couple and their two kids. And a black woman sitting next to me, rolled her eyes and gave a nasty face and turned the other way after staring them down. I’ve seen the same with white women when they see a white man with a black or Latina woman. My aunt has been married to a white man for 30 years and STILL has issues with her mother in law and racism. WHY??????