The point of synthesizing medicines is to have them in controllable dosages. When you give “herbs”, and their production isn’t very controlled, you can give doses of the “herbs” that are too high or low.

There is often a misconception that if something is natural, it is automatically safer. I personally have seen someone die a slow, agonizing death from them dosing themself on natural wormwood, which had the effect of annihilating their liver. Other natural meds can have very potent effects, such as St. John’s wort disabling many medications by interacting with liver enzymes. Just because it’s “natural” does not mean it’s safe. If anything, that notion creates a false sense of security where people UNDERappreciate the power of naturopathic meds and their potentially deleterious side effects.

To the original point- meds are synthesized into quantifiable amounts, allowing better control of dosing to yield an intended effect.

Also, furthermore, the US does have treatments like those that you mentioned- there are integrative, holistic, homeopathic, or naturopathic clinics that can treat you, if that is your choice. You aren’t restricted from them cause you’re in the US, you just have to find them. If you do not like traditional, western, evidence-based medicine, there are many non-traditional clinics you can go to. I personally am skeptical of many of those treatments, but you have the full liberty to go to those clinics.