Selling medical drugs is very big business. The answer is quite simple really. Ample medical research regarding fasting, nutrition, physical activity was carried out in 1930 through to 1970 and amply reported in mainline, recognised medical literature. However it has never been popularised and was kept away from the public. Hygienic procedures cannot be patented and sold over the drug counter.
Licensed doctors are easy to control.
U.S. physicians are captive audience for pharmaceutical advertising. This applies to other countries as well. They learn which drugs to prescribe. They do not learn of alternative procedures and perhaps better ways of caring for their ill patients. If one were to seek this information for himself he finds himself outside the realm and benevolence of his professional guild.