Must be something with the "magic pill for everything" PR that is popular in USA. Goes hand in hand with non existing public healthcare, so "market can handle that".
From branded medications to diet books, "health" foods, and trends ad nauseam, there's a pervasive culture of cure-all objects and systems.
Then again, we don't have fine physical understanding of most mind disorders or the medications we use to treat them so if your doctor is effectively throwing darts at a board then why not internet strangers?
Everyone in this thread trying to say general ignorance is something Americans have a monopoly on is silly. It's a human condition, nothing to do with country.
Many wealthy European countries have a much more suspicious attitude to health vendors. Then again we often ban their advertisements.