I assume by helping normalize them into the mental model of “CPR patient” which overrides all other aspects of social propriety. “Don’t touch boobs without permission” is a big rule so plenty of people are going to have to manually override it in the decision making if you haven’t been desensitized to the fact that some CPR patients have them.

I also suspect that the awkwardness of what to do with them while doing chest compressions is helpful, especially ones big enough to move around as you do them.