They may have demonstrable benefits and they may not. I personally don't use these treatments and don't hold much hope that they will ever be demonstrated to have much healing power, but the truth is that they are scientific unknowns. Nutrition, however, is not an unknown. An incredible number of scientific studies demonstrating the beneficial effects of essential nutrients on various diseases have been performed. Many more need to be done, but the nutritional basis of disease etiology is not questioned by rational people today.
Nutritional deficiencies cause disease.
Since most doctors have very little nutritional knowledge, they are unable to help people suffering from these diseases other than by offering drugs and damaging medical procedures. This is not the result of doctors not wanting to help, it is the result of the lack of proper education in medical schools. The curricula of medical schools is probably 30 years behind science and the average physician has been out of school for an average of 20 years with no remedial education. This means that the average practicing physician is practicing medicine at least 50 years behind science. Since most of the science of nutrition has been developed in the last 50 years, this means physicians just don't have this information to help people.