Do you mean because these herbs aren't cholagogues, or don't cause the liver to expel bile? That is an interesting way to describe it. I would frankly like to know much more about liver detoxification apart from the flushes. Partly because it is good to know in itself, and partly to help other people that I know would never do a flush.
My personal favorite amongst cholagogues I've tried is roast chicory root. Tastes very much like coffee, and I can feel my body's reaction to it.