This is to desensitize Americans so they will be unable to determine what is fake from something that is real.
People will just think “silly me, it is just the military playing games again”!
Occam's Razor
The military has more than enough room to do this training in complete seclusion just as they have been doing for decades. This is being used to set up a diversion so that any resistance will be caught off guard.
I'm thinking this is a long term plan to do exactly as others have stated. To get the American people used to seeing military maneuvers so they will not realize exactly when it's no longer a drill.
This shit is getting scary folks. If you are not paranoid now, you should be.