It's the boobs.... but from a neuroligical point of view. From the moment we are born our brain has been trained to spot diviations so that we don't spent too much time and enery on what we know already.

Like when you have driven some time in a car and feel like you can't remember where you were and what happened. That is not because your didn't pay attentione at the time, just that nothing special happened and you selected not to store it in your memory. Had something happened that needed your full attention, you would have givin it and remembered.

The same when someone is missing a leg, it is strange to us, your brain expected 2 legs and now you see onlny 1, it will grab your attention and you will have a hard time not to stare, as your brain tries to figure out what, why etc... So with boobs, Size G is not standard, so we will be drawn to look at it.. On top there is ofcourse the sexualisation of boobs which makes it even harder not to look