White males, as a group, are fairly intimidating to other groups (and often behave in exclusionary ways).
This is not an issue of "reducing to single characteristics", but of power imbalance. I can't speak for other minorities, but a lot of women are experiencing discrimination from men in some way in some place in their lives. Try looking at #YesAllWomen on twitter if you want more details.
And so it's meaningful to set an example that says "While this profession currently predominantly male, we do accept minorities, and there are many non-white/non-male people in our industry who succeeded". That is what the role model part is about - clearly communicating that it's not a clique. That privilege is at least somewhat addressed.
If there were black privilege in the NBA, yes, it'd be a lot scarier for white athletes to get in there. Looking at the odd fact that by far most quarterbacks are white (75% of them right now, and the fact that it's so low is celebrated), I think we're far from that point.
But even if we leave out the debate around privilege and pretend for the moment that it doesn't exist: Being in a minority leads to a lot of shared experiences. A creative woman interested in CS, but not in the field has more in common with other women than she has with a guy interested in exploring CS.
There are more shared experiences the longer you share that interest, and the differences vanish. But at the point where it's about getting into CS, these differences matter. And seeing somebody who is "just like you" matters, on a psychological level.