[Huey14]

I was being specific to Blackwater but I don't really like the idea anyway so I'll answer it.

Because:

Having a blimp sitting in the one position creates dead zones where the cameras can't see;

(To expand somewhat on the last) The fixed position means they know where it is 24hours a day, which means they know where the tether position is which in turn means the cable can be destroyed and the balloon is then about as tactically helpful as Mary Poppins;

If not tethered, balloons travel at a speed that means you can see them coming, and hence avoid them.

Not to mention they're a hazard to aviation-both military and civil (though I'm guessing there's not many people playing cessnas around downtown Baghdad LOL).

Maybe I'm just a traditionalist and don't like things without wings.