The cavity of your mouth is shaped in such a way as to circulate air that way.
It’s called retronasal olfaction.
Or if there are any, there are very few.
It’s partly because of the way our bodies are shaped. Makes it so smells can travel to our nose much more efficiently from the inside of our mouths.
3x3cm. About the size of a quarter.
If that’s damaged, you lose a great part of your ability to taste food.