I'm not sure why. I'm still fascinated with them. For me, it's just another one of her erogenous zones that I need to stimulate in order for me to be a successful partner. In any other setting, especially professional ones, it's "eyes up buddy".
I could be wrong though. Like zab said, we really don't know what it's like. That's where my point of actually talking and understanding comes in. "What makes you feel good, what is uncomfortable for you?" type of stuff that leads to further conversation about how they actually work.
Like I said many times, I was with my ex for a long time and we weren't shy about anything. We shared 1 bathroom with clear glass shower doors and nothing was off limits.
My current special other is an ER nurse so, there's nothing she hasn't seen or is afraid to talk about and I really enjoy picking through her brain.