This housefly was sitting still for a long time. A very long time. Are you asking me the question “Why?”? This is a natural behavior exhibited by houseflies, just after the sun rises. This habit warms their wings up and makes them ready to fly.
While capturing a two-tailed spider just a few inches above this, I noticed that this housefly would look wonderful when captured like this. I decreased the aperture to the minimum just to bring all the attention to this fly.