Why are people in criminal detention not allowed to see their relatives?

Hello: According to the criminal law, after a criminal suspect is detained by a public security organ, he can get legal aid from a lawyer. Explain that with the consent of the case-handling unit of the public security organ, you can only meet with your own lawyer. You can't see your family during criminal detention, one is to find out all the criminal facts, and the other is to prevent collusion and transmit relevant information.