I think its apart of a media campaign to highlight the best parts of the agency to the public, which can be used for attracting talent, convincing voters that the agency is good, and convincing leaders the agency is necessary.
Additionally, its also a defensive move against other powers that want to discredit the NSA and sway public opinion. Many security professionals talk about cyberspace being the new territory for warfare, and there is a significant amount of astroturfing, manipulation and falsification of information which occurs in social media. No one else is going to try to make the NSA look good besides the NSA.
I'm not saying I agree or disagree with the NSA, just that the basics of the increased media coming from their office is to attempt to make the NSA look better to all parties who have some level of power over them.