What is the end result? You go up to someone who isn't a minority and tell them that even though they did everything right and were in the top 100, you choose a minority who was in the top 500 but not the top 100 over them due to their status as a minority? What will the impact of telling them that be?

Of course, no employer (that I have ever seen) is that open. We share a common expectation that the people who qualified but were passed over won't be told. Maybe an open ended promise of "next time". All this does is allow the same effects to be diluted to anyone who might have been impacted. So now even those outside the top 100, even those outside the top 500, consider there is a chance they were impacted by such an action. So while the impact is less than telling the person passed over, you now have more people feeling it.

And this does seem to be a damned if you do/damned if you don't, because even if you did create a top 100 ranking and used it to promote, that would be influenced by subconscious biases and other factors based on minority status and people aware of that who didn't get promoted would also be negatively impacted.