Because non-whites want it that way.
I heard that UCLA or USC (or one of those colleges in Southern CA) was having separate Hispanic and black graduations, because the Hispanics and blacks wanted it that way. They're the segregationists.
I’ve always noticed that people tend to segregate themselves. Look at any social situation. Like tends to stay with like. Not attaching anything to that other than it’s just an observation. People tend to choose that (segregation) for themselves - and when they do, why should government step in??