Because if that information were released it would cause significant damage to the country. Why on earth is my company's TLS private key kept a secret from all the employees?
> Why on earth is my company's TLS private key kept a secret from all the employees?
A far more adequate analogy would be a company spying on all of its customers and employees, and then lie when asked about it.
Companies regularly monitor employee activities on corporate networks and computers. They have a responsibility to make sure employees aren't using the company's assets to break the law, steal corporate information, leak private information, or irresponsibly download and run malware. If you tell employees exactly what the company is monitoring and the exact methods they use to monitor activity, the monitoring becomes useless because people will subvert it.