Your Mother, It was created by scientists to be used as a anesthetic, the person who created it is most likely embarrassed by its terrible downfall and will not step up to it
I cant see why it should be unless one has some sort of fetish about certain types of shoes or clothing during or prior to sex.
That's just the way God made you! :) (if you want sensitive,the lips are 100X more sensitive than your fingertips. i tried my boyfriend, and he loved it!)