Evidence must be painstakingly accumulated and analyzed before an accusation can be made. Even a psychologist who knows the syndrome well can't prove a particular case without a physician's painstaking analysis of the medical record. As a physician, you certainly wouldn't make this diagnosis the first time you encounter the child or the family. It's something you would build over a period of time. The expectation of legal action may dampen suspicions.
Nobody wants to get involved because there's fear of litigation.
Inside the Strange World of Factitious Disorders.