Simple. It isn't falsifiable, it isn't testable, there's no objective evidence to support it, and in order for it to be called "science," the word must be stretched to include such concepts as astrology and the discarded "ether theory" of light.
From the cross of Behe:
Q Under that same definition astrology is a scientific theory under your definition, correct?
A Under my definition, a scientific theory is a proposed explanation which focuses or points to physical, observable data and logical inferences. There are many things throughout the history of science which we now think to be incorrect which nonetheless would fit that -- which would fit that definition. Yes, astrology is in fact one, and so is the ether theory of the propagation of light, and many other -- many other theories as well.
Q The ether theory of light has been discarded, correct?
A That is correct.
Q But you are clear, under your definition, the definition that sweeps in intelligent design, astrology is also a scientific theory, correct?
A Yes, that's correct. And let me explain under my definition of the word "theory," it is -- a sense of the word "theory" does not include the theory being true, it means a proposition based on physical evidence to explain some facts by logical inferences.
Behe admits that by scientific standards, ID doesn't qualify as a Theory, which is why he needs to redefine the word to include "guess".
Falsifiability does not define science, but is only one of many tools it uses. There is ample supply of organized matter that behaves according to predictable laws from which one may reasonably infer intelligent design. Incorporating such evidence in no way necessitates adopting the premises of astrology or other disciplines related to theology or religion.