Visible crew/equipment: When we first see McClane on the snowmobile, marks from the camera snowmobile are visible. (01:27:20)
Visible crew/equipment: When we first go to the Annex Skywalk, the SWAT team are walking with the guy from the tower and he is talking on a radio. In the mirror behind them you can see the boom mike and operator as they walk.
Answer: Because the police were moments away from arriving at the scene. They needed as much time to get away without being tracked. Every moment counts. And a target rocking about a few hundred feet in the air doesn't seem to be such an "easy target".
XIII