NDAs are not unique to the current administration nor the worlds of politics and business in general. It is a way of protecting inside information or trade secrets.
In the military, this is the reason for security clearances, which give access to certain levels of information, depending on the level of clearance. And disclosure of classified info is a crime.
On point, TLC has been notorious regarding enforcing NDAs.
Edit ... I guess the real question is why anyone would hover around Amy.