Again, Snowden leaked a single extant program that was potentially illegal. All he had to do was blow the whistle on that program and the other possibly program that had already been shut down, and we wouldn't be having this conversation. Instead, he told China what systems the US had compromised and additionally claimed the US was doing a bunch of illegal things that his documents did not support, causing hysteria and helping Trumpism.

The thing that makes illegal programs almost impossible to hide are the reforms after the Church Committee, including SSCI oversight and whistleblower procedures and protections.