Why do some parents want their children to act like an adult when they hit their 30's even if they have a disability like cerebral palsy?

Confusing question: An adult is an adult.The majority cerebral palsy patients have no cognitive impairment that would prevent acquiring adult self monitoring & awareness skills. Those that are mentally impaired need help with these issues but can learn them over time. Why wouldn't a parent want his kid to develop acceptable behavior pattern.

Want best for child: All parents want the best for their children. When a child has a disability like cerebral palsy and developmental deficits, parents are can be disappointed and use denial about their child's challenges. Ultimately, it is an effort to somehow get their child to be like others their age.