I understand now.
I think a basic reason for this is that when making pigtails for handles, the top pigtails are always longer than the bottom to lay the leading edge back a bit. Basically, instead of extending the top lines via pigtails, the top lines themselves are made longer.
And, as John mentions, if you had longer top lines and pigtails, you could adjust the handle setup to compensate for the difference in length. The smaller the difference between the tops and bottoms, the less you have to compensate. So, if the difference is 12 inches, it may be difficult to compensate for it, whereas a difference of 2-3 inches is easily compensated for by pulling in or letting out the lines by a few knots. As long as the tops are the same and the bottoms are the same, there will not be any issues with, say, the kite turning on its own.
All clear now Watty thanks so much