Probably because it's impossible to respond to ideas like these because nobody's actually taken the trouble to do something simple that would allow them to be examined. By this I mean actally giving a rigorous definition of these terms. All of the definitions of irreducible complexity that I've seen, for example, are either circular or they rely on argument from ignorance. They say that something is irreducibly complex if there's no way it could have arisen without design. How do you recognize this? What property tells you that something must be designed? Why, irreducible complexity, of course! The other definition I've seen is that a system is irreducibly complex if it can't function if any of its parts are removed. How do we know it can't function, but function more poorly or function differently? How do we know that the original system didn't originally have a different function from that imputed to it by the ID proponents? Adding another part might allow it to perform a different function. These, therefore, are arguments from ignorance or incredulity. Essentially the ID supporter says that these things are irreducibly complex because they can't see how they'd have evolved naturally. BTW, reasonable evolutionary mechanisms have been proposed for systems that typically are stated to be irreducibly complex. If these systems are shown to actually have evolved, would they still be irreducibly complex? Or would ID proponents then state that they aren't irreducibly complex after all?
This is a moving of the goal-posts. When arguing for evolution, the goal-posts are likelihood, but when discussing the arguments against evolution (like irreducible complexity) the goal-posts are a proven impossibility based on purely imagined sequences, no matter how improbable.
Creationists are not allowed to state possibilities that may not be entirely likely, but evolutionists are. Therefore, evolution is true and creationism is false.