Because it's a beneficial training tool to use the hands to guide intent.It becomes far more powerful as your training progresses. Of course the intent is in the body but it is in the limbs as well.
... Thinking it must be like what's going on at 22-24 seconds in this clip.
Is it right?
These are some thoughts:
It's how to 'bridge' or 'graft' onto a second set of intentions, until (i assume) eventually it's a smooth transition, without the need for the hands.
I noted that in the original TenChiJin that I saw, with Akuzawa does not amplify this movement in such a way..
In my own mind i think of it as bringing two movements with knife-edges together, until the transition between them is easy.
All, for what it's worth, of course.
p.s. I've finally found a clip of shiko.
Gave me some ideas. Thank you very much to the original poster: cris693.