The biggest reason for the variations in temperature is that chicken, turkey, and duck are very different meats. They have varying degrees of water content, collagen, and bone structure. Sometimes it is easier to substitute one poultry for another than others.
But another reason why there are so many different times and temperatures is that, like eggs, there are several ways to manipulate time and temperature to get to the same result. So for example, I could cook a chicken leg at a high temp for a short amount of time, and there would be an analogous low temperature that would achieve the same result over a longer period of time. It‚’s a sliding scale. There isn‚’t just one temperature and time to end all temperatures.