This is one due to our changing life style.
We have moved much from home made items to manufactured products. This is same whether it is food, cosmetics or medicine. People naturally prefer to avoid physical labour and want more time for entertainment and comfort. The more the convenience and comfort we get the more we want still. So it is like a flywheel.
Until my father was alive, we were preparing herbal medicines at our home only. The Ayurvedic doctor(or vaidya) will give the prescription; the herbal ingredients will be either procured from home or around , and those not so available will be bought from the native herbal medicine shops. That needed knowledge about the herbal ingredients,needed laborious preparation to clean and make them ready to add and make the medicine. Most preparations needed longhours in boiling, evaporating, concentrating, filtering, mixing etc and the same may need many cycles of repetition. Some medicines may need gestation time or waiting period before it can be taken for use. Now people have many other tasks and cannot aford to spend long hours in medicine making.
The second reason is many of the herbs have started vanishing due to deforestation and denudation and destruction by expanding human habitation.
After all this, the herbal medicines do not work as wonder drugs for instant relief,unlike the allopathic chemical medicines that give instant comfort to the patient. As today's life style does not convenience us to rub a smelly and sticky balm many times to get relief form even a small headache, we prefer to take a chemical ingredient tablet instead and forget the pan within a few minutes.
Last but not the least, as of now there is no comprehensive testing facility or statute to have a proper and truthful test to evaluate the quantum and quality of the ingredients. Due to the difficulty in procurement of ingredients and long processes,the ready made or manufactured herbal medicines are relatively costly too.
All this makes people to avoid herbal medicines in the modern days. However now there is a reverse trend catching up due to the awareness of the harmful side effects of the medicines made with chemicals.