In the past few classes we have talked about food chemistry. It seemed like I have the least knowledge of food and cooking in the class. However, I do cook sometimes too! with my microwave oven which is the only thing that I use in my kitchen.
In a conventional oven, the heat has to migrate from the outside of the food toward the middle . You also have dry, hot air on the outside of the food evaporating moisture. So when you put a bread in a conventional oven, the outside can be crispy and brown while the inside is moist.
In microwave cooking, the waves penetrate the food and excite water and fat molecules pretty much evenly throughout the food. No heat has to migrate toward the interior by conduction. There is heat everywhere all at once. The whole heating process is different because you are "exciting atoms" rather than "conducting heat."
So in a microwave oven, there is no way to form a crust. That is why microwavable pastries sometimes come with a little sleeve made out of foil and cardboard as we can see in a hot pocket. You put the food in the sleeve and then microwave it. The sleeve reacts to microwave energy by becoming very hot. This exterior heat lets the crust become crispy