There is a simple reason why- a couple, actually.
Let's say I made up a herbal tea for inflammation. I sold it to 20 people with various chronic pain issues- back pain, arthritis, joint pain, etc. And all 20 found relief. Many were able to reduce or eliminate their prescription pain meds. You would think I have a sure fire winner. I do, but the FDA will not allow me to make any claims of therapeutic benefit without conducting clinical trials and receiving FDA approval. Even if my tea helps 500 people, I cannot claim it relieves joint pain or any other type of pain.
The other problem is, I have nothing to patent. Even if I did spend the countless millions needed to gain FDA approval, I would not have exclusive rights to my herbal tea. You cannot patent medicinal herbs. It's like trying to patent sparkling water.
There is an Amish guy who is facing jail time for selling some sort of anti-inflammatory salve made out of chickweed or something. He claimed it reduced inflammation even after being warned by the FDA not to. I don't know if it did or not, but he sold a whole lot of it. Now he is paying the price.
Navigating through the world of natural remedies is tricky.
I make and sell all sorts of herb and essential oil blends.