Why fewer operations on weekends?
Your data TELLS us that the airlines schedule fewer flights on the weekends, from which we can INFER that there is less demand for travel on those days.  (The numbers of cargo flights at PHX are dwarfed by the numbers of passenger flights there. The data at a major cargo hub like MEM or SDF might be different in that regard.)

To what extent that is driven by business travelers or leisure travel patterns, is beyond your data, and might even get into some fairly complex data and calculations that USAir and Southwest and others use to build their schedules.