What's silly? Thinking that when the NSA finds vulnerabilities in public software or algorithms, they keep them to themselves instead of advertising them? What, of course they do, it's silly to think they'd advertise them! That's their job.
It depends, they have to keep in mind that they're setting up a risk that foreign adversaries will exploit the same flaws. You're trying to square the circle - you want to have your own country's infrastructure, not all of which is under your control, secure from attackers and at the same time have it open for control purposes. And inevitably trade offs have to be made.
The driving force behind encryption becoming widely acceptable, in business terms, for instance seems to have been e-commerce.
Turns out the NSA has cracked a bunch of internet encryption, and, yes, they kept it a secret they had done so, as most would expect they would. Until Snowden.