It has to be taken over a large period of time to get the blood and lymph, and intestins cleared. Most wont stick it out, all want a quick fix.
From my experience it is not only a question of time, it is a question of high enough concentration in the body during a high enough time.
And most people are not ready to stop eating for one day, so if one blends foods, drinks and the anti helminths substances in the herbs, then the anti helminths substances are in a lower concentration in the digestive tube and in the blood. Hence the lower killing power.