@Sophistifunk
Because that bowl is unsafe for microwave use (it absorbs the microwaves).
See this
https://www.wikihow.com/Test-if-a-Dish-Is-Microwave-Safe
for a simple test to see if an item is safe for microwaves.
I will also note that some plastic plates and bowls can leach when used in a microwave and will try to poison the food.