Green arrows on Tucson traffic lights

Now why are these things used in the middle of the night?

You sit at a light. No one in sight at 3 am.
The other way finally turns red...But wait!
The green left turn arrow comes on, so you sit for another minute.

Anyone that needed to turn already did. Do they really need the arrow? Was there really a car sitting there the whole green light, waiting. With no oncoming traffic the whole time. Who is in charge of these things?