Because in general the military in the US is far more secretive than they used to be. In the past there was a certain expectation that the DOD had at least some obligation to keep the public informed of what was happening within our borders unless it needed to be heavily classified. Over time that's changed to where now they keep secret even mundane things that directly impact Americans, and even when the information is highly generalized and/or well known because we have things like radios and cameras too.
On one hand I kind of understand it - the world is slowly coming to the realization that information is the most important weapon in both war and peacetime, and no matter how inconsequential any piece of data may seem the ability to aggregate, cross-reference, and so on mean any shred of information could be dangerous. But at the same time that approach to the world doesn't really allow for a free society. I think the US government has made pretty clear they're happy to subvert or ignore American ideals to protect it (hell, the whole western world is like that now - see May's bald statement that no human right is too important to throw away in pursuit of bad guys).
