People who are typically drawn to computers are often not very good canidates for the military lifestyle. And to become good at Securing systems or hacking them.. you need be breath, eat and sleep computers (especially hacking them).
Hacking skills are not taught in schools and working for the goverment pays c@rp.. why would someone who spent years developing highly saught after skills work for the latest cyberwarfare agency when they could make big bucks in the private sector.
There are plenty of highly skilled security folks out there "Defend the nation" to. I dont see any real recruitment efforts going on that are worth while.