OP's point is still important, though: you're talking about the wrong kind of diversity. If you go to a school with a bunch of kids who grew up in upper-class neighborhoods in Washington, D.C., who cares if a few of those kids have black skin? They're contributing ~nothing to the diversity on campus, because they grew up in the same place and come from the same income level.

On the other hand, if your admissions policies make a point of drawing from many income brackets or many countries, suddenly you have a whole world of people who you likely would never have associated with and who are actually different than you in meaningful ways.

Country of origin and socioeconomic status are a much bigger deal when it comes to diversity than race, because race isn't real. It's a proxy for things that are real, and continuing to use it as a proxy perpetuates a subtle form of racism.