"Probably somebody in their life told them they couldn't do math."
ChildUp Early Learning Key #2: Talent is made, not born
All Children are “gifted” for nothing in particular; they are gifted for “everything”. The idea that some lucky Children may be talented from birth is a pernicious myth. A focus on effort and practice, rather than on intellect and ability, is much more encouraging. Children who believe that talent and intelligence are made, not born, get better results in any domain.