I don't get why a private University can't decide who it wants or doesn't want to attend its school regardless of the metrics it chooses.

For instance, I don't think that matching a Universities demographics to the "national" or "global" demographics is likely to produce highest caliber candidates. What if Jewish and Asian candidates consistently outperform other candidates, why shouldn't a private school be allowed to accept more of the candidates it thinks "deserve" it more?

If people don't like the policies of institutions that do this, or think they are ineffective, over time other institutions will outcompete/outperform them.