I think it's a little more complex than a simple cure for each ailment, but we are sold that idea because it earns money. You can be sold a drug that helps with symptoms and seems like it's curing you, after all. It is therefore more profitable to not educate the public on how they can stay healthy or return to health.
The closest thing we have to a panacea is our immune system. When it's functioning optimally it can fight off most pathogens, but when it is overworked by a toxic environment then it begins to fail us and the damage to our cells brings us to chronic illness.
Plants are like medicines in that they can help with symptoms while we try to find the underlying cause and get back on the path to health. Sometimes the damage can be too much if our DNA has been damaged, so then we can only do our best to slow and mitigate the damage to feel a little better.