Because the benefits of diversity policies are about improving minority access to resources (where systematic structures unfairly deny them access) and increasing free exchange of information, ie, culture, backgrounds, etc. My friend does not really fulfill that role. But he would be stupid to put white on the application, because institutions are looking to increase diversity, as well they should be, and the easiest way for institutions to do this, whether accurate or not, is by looking at which little box you ticked. That may have been a run on sentence. So yeah, don't put white, unless you are white. I think that is pretty straightforward.