How did massage therapy once championed by a number of influential doctors become considered alternative?
A group of physicians in the late 19th century advocated for the inclusion of physiotherapeutics, including manual therapy, as a third branch of medicine(alongside surgery and pharmaceutics). Other physicians shunned it as the purview of charlatans.
  In the end, physical modalities did find a less central place in the conventional establishment, becoming a specialty called physical medicine and rehabilitation. The profession of physiotherapy/physical therapy, organized by physicians’ assistants, found a place as allied health care. Independent massage practitioners, despite having similar skills to early physiotherapists, remained in tradition of drug-less and natural healing and were left with the status of alternative. these outliers became the nucleus of the emerging massage therapy profession.
‘Excerpted from The Emergence of the Massage Therapy Profession in North America’ Executive Spa and Massage