I just told you the practical purpose, not being ready to wipe things so easily. Falls drop zone is WAY more precise than airborne so it's a lot easier to drop them in behind the lines.
And the squad size isn't the reason for that difference, because the Soviet airborne drop is more precise too. Unless it's been changed since i last tested it
USF paras can drop with pin point accuracy on beacons, falls drop seems to be effected by LOS.
Its large when the drop is FOW and small when one has LOS in area.