My guess would be a computer system is monitoring demand and changing routes dynamically throughout the day.
It is aware of the "estimated time" between legs of the route, and when what driver comes on or goes off shift. It likely organizes the route in order to maximize throughput while decreasing fuel waste as much as possible.
My guess is the driver probably has a pretty good idea which stops they will be hitting for the coming 2-4 stops, but their schedule changes depending on reported/estimated demand.
Just guessing though.