To limit the probability of an excessive area of glass in the door, which could lead to the glass being unable to resist wind and impact loads, which could lead to glass breakage, which could lead to harm to persons.
To limit the probability of an excessive area of glass in the door, which could lead to the glass being unable to resist wind and impact loads in an emergency, which could lead to glass breakage, which could lead to delays in the evacuation or movement of persons to a safe place in an emergency, which could lead to harm to persons.