There are non-compete clauses for the guy making your sandwich at Jimmy John's. Why do they exist? Because how to make a particular sandwich by some predefined script isn't privileged information, so you need some other way (possibly futile) to prevent others from disclosing it.

But the CTO at the NSA with access and intimate knowledge of the entire body of classified information in his field of work, selling his services to the highest bidder in the exact same field? I guess if the client was Huawei he'd be rotting in prison by now, a traitor and spy.