Of course it would be big time. Nobody is arguing it wouldn't
However, that's not how media rights holders think about it. Sports is the last appointment viewing endeavor on TV, everything else gets watched on demand. Thus it makes sports the most valuable real estate for TV advertisers because they know people will be in front of their TVs at broadcast time.
So the networks know that Duke, UNC, and UK will draw viewers with or WITHOUT each other. So, they would rather have 3 big draws than 2. It makes sense if you think of it from a business perspective. Advertisers appreciate it as well.
Just using myself as an example, I will probably now watch all three games instead of two. I will watch UNC and Duke to cheer against them and UK to cheer for them and this will be done a million times over by others.