Why is judo's Katame-no-Kata so free-form relative to Nage-no-Kata?

Question

The first two kata taught in judo are Nage no Kata (throwing forms) and Katame no Kata (grappling forms). Here is also a second Katame no Kata video with different escapes for the first pin kuzure kesa gatame.

These are excerpts describing Katame no Kata from Judo Formal Techniques by Tadao Otaki and Donn Draeger published by Tuttle Publishing, Boston, 2001 p. 130-131:

Uke has the role of honestly trying to esacpe from Tori's applications of grappling techniques... These escape actions are not defined as only certain correct methods. Such rigidity is not required by this kata; in this respect this kata is more "real" than the Nage no Kata.

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Practicing this kata with reliance on certain prescribed escape actions by Uke, and only those actions, gives it an unnatural flavor. The kata is thereby reduced to an exercise in purely anticipated movements and subsequently has less training value than intended by the founder.

In correct practice, Tori does not necessarily know what precise methods of escape Uke will attempt. While the avenues of escape are commonly more or less expected by Tori, and there are some escape actions that are best, they are not stereotyped and prearranged as to their identity or the order in which they will be attempted by Uke.

In Nage no Kata, the movements of both partners are precisely prearranged and anticipated, including how grips should be held, the number of steps that should be taken, which foot moves first, and uke's reactions. Why is this level of prescription avoided in Katame no Kata? Or why could not Nage no Kata be similarly free-form?

Answer 1

Throwing someone is difficult and depends on particular openings, balance, and grips; staying standing is the easier "default". In contrast, pins are the opposite: the escape is difficult and depends on particular openings, weight distributions, and grips; staying on top of someone who has already been pinned is the easier default.

Standing opponents, by default, stay up

Throws, such as in nage-no-kata, are contingent on uke's specific actions to provide a set-up. If my opponent is pulling their arm back and sitting into their heels, I need to kouchigari rather than seoinage; if they are on their toes pushing into me with an extended arm I cannot force the kouchigari but must seoinage. Their attacking action determines my throwing action.

Pinned opponents, by default, stay down

Pins, such as in katame-no-kata, are largely indifferent to uke's actions. Mostly because pinning techniques are effective and get to be established first, it is difficult to counter them. Once tori has a pin in place, it should be effective without respect to uke's escape attempts, because they were designed to handle bridging, shrimping, sitting up, and attempts to establish frames.

We are of course discussing the ideal case. No pin is dependably reliable against diligent escape attempts, just like no throw can be relied on to work simply because the set-up has been given. Advanced pinning strategy means switching between pinning techniques as uke resists, and elite throwers can insist on using a particular technique even without the necessary opening. But we do know that these two classes of technique are on opposite sides of a spectrum.