I do not know why either, but maybe the great man thought he would be repeating himself.
Possibly he believed 2- J -3 and 7- 23 were sufficient.
If it is not a straight line, is it a circle?. No, but that does not make it a straight line either. Depends on how thick the line is !.
Arc or Angle, Rim or Spoke, Hit or Swing. Interesting topic.
I am sure someone must know why.

In reality the Straight Line Delivery Path is never a Straight Line for more than a few inches at most.

I believe it looks more like a tilted oval pointing at the Ball (or alternative Aiming Point). Also, your hands tends to be closer to your body when using a Striaght Line Path.