Adherence to "evidence based" therapy guidelines is typically enforced via malpractice claims. Obamacare tried to introduce incentives for outcome measurement/tracking and evidence based care by either cutting or supplementing medicare reimbursements, but even that has been difficult to implement nationally across the 5-7 most frequent and costly conditions and procedures (e.g. acute myocardial infarction, COPD, knee replacement, etc).
While the FDA's regulatory approach does slow the pace of innovation, they exist for a reason -- I acknowledge that GP is not calling for any policy change. Snake oil salesmen were a real thing, and still abound in the valley albeit in different form.