Fear and / or Embarrassment.
This question hit home for me. I was born an odd child. Extremely strong, I didn't seem to need my mother, or had already received the message that since I was not a boy, I was not what she needed to solidify her marriage.
I cannot remember any affection. I was left solitary.
I am psychic, have always been unnaturally strong, and have a way of peering into the soul of a person.
At four years old I learned to read.
About that same time, I remember how I stood in our living room as Dr. Martin Luther King, Jr. gave his famous "Dream" speech. I stood in front of that television screen and wept heart breaking throbs. I remember seeing people of all colors marching, and felt an urgency to be there and to help.
At age ten, a lovely librarian put "Bury My Heart at Wounded Knee" by Dee Brown into my hands; again I felt that call that cannot be ignored.
Four years later would find me in front of the BIA, protesting the actions of war against the Oglala Sioux Tribe at Pine Ridge Reservation.
Two years later I was petitioning our President and Congress to create an agency that would give the people of the United States, Environmental Protections.
Today my urge to help People and our Environment has not lessened.
To finally answer your question, I think it is because those children are meant to do things that a typical caring parent trying to fit in would not allow.
No one wants to be "different" or stick out from the norm.