why does my awd ford fusion spin just one front wheel when I am stuck

The wheel that is not stuck will spin because is "loose". There is not enough power to move both wheels even if it is AWD. Remember, this is a car, not an all terrain vehicle specifically designed for off road driving. Try to avoid driving where you can get stuck.

AWD these days is pretty sad because you rely on electronics that decide if they will let you have AWD or not. Turn off the traction control if you can.