It’s more subtle than you might think. How do you keep the light from blinking off and on around dawn and dusk when light is near the threshold and variable? What about snow accumulating on the sensor in the winter? How do you switch lamps rated up to 1000 watts, possibly with inductive ballast? And how do you do it cheaply and reliably, since it’s expensive to send a guy up there to replace them when they fail?
Extra bonus insight: why do street lights come on for a while when power is restored after an outage during the daytime, then switch back off shortly afterward?