Remember that Snowden always said he was ready to come back to the U.S and be trialled, as long as the trial wouldn't be a secret trial. Those who created the laws for those secret trial where not the CIA or the NSA, it was politician.
The same way they made it so that it is forbidden to talk about the programs of certain agencies, even for law maker, meaning they approve programs without debate, with only a few senator knowing what the program is even about.
They created those laws, not the NSA, not the CIA, they could choose as easily to remove them. But it is too useful for them. The NSA can create a massive surveillance network that serves them without having to ever disclose it to the public.