When cooking food in a microwave, why is it more important to rely on the internal temperature of the food rather than on a previous cooking time?

When cooking food in a microwave it is more important to rely on the internal temperature of the food because microwave do not adequately kills pathogens that may be in food.  Microwave normally penetrate food to the depth of 1 to 1.5 only. In thicker foods, microwave doesn't usually reach the center of the food, the un-reached part normally cook by conduction.