So I suppose the more accurate question to ask would be, from my framework, "why are field-dynamics characterized as irrational, and object-dynamics as rational?" My answer is that, when you examine the dynamic aspects of information,the observer has two things to focus on, two areas of dynamic perception, if you will, from which he can obtain information: the outside world, and himself. His perceptions of the outside world can change instantaneously; he may shift his focus to another target and thus, the perceptions of this outside world are considered discrete, or rational. The things outside himself which are changing, which can potentially affect him, are things he must attempt to gain control over, things he must harness or reign in. His perceptions of his own constantly changing reactions and involvement are, however, contiguous, existing in one constant stream, inseparable from each other. That which is inside himself, and is inherently changing, must be allowed to change freely; thus, irrational.
It is this emphasis on IM being the properties of the actual mind's focus, rather than simply methods by which reality can theoretically be broken down, that convince me both of the value of Jung's work in interpreting Socioncs functions, and of my particular definition of objects and fields. I am, of course, open to your interpretation, if you would give me your own answer to such a dilemma.
To apply the same formula, with regard to the theoretical assumptions of the model and nature of the functions that I outlined earlier, to this question, I would change the question to "what makes field-statics rational, and object-statics irrational?"
Well, if we go again with the assumption that the divide in perception is of that which is inside the self, and outside the self, then we can easily see that the things which we consider as static and unchangeable outside ourselves are those things which we have no control over, which cannot be dissected or broken down; thus, they are irrational. Conversely, the things inside ourselves which are static are those things which we must maintain constant control over, to keep them in place and maintain their boundaries; thus, rational.