Nipples are not just embarrassing. They can be quite dangerous. Much like certain male organs, you could poke an eye out with one of those.
In any case, sexy running is important. As a former male (former in the sense that I have now reached an age where sexy is far less important than a nap), I can remember watching sexy women run. While I was unaware at the time that the sexiness was augmented by these inserts, my life would have been less joyful had that sexiness not been present.
Thank you for the education.