Why do doctors almost never suggest natural cures?

Several Reasons: Doctors (md/do) are trained in more of an evidence based medicine. Unfortunately, there are not a lot of good scientific research supporting natural cures. For those treatments that do have some research backing, some doctors may not be experienced in using them or have experienced better results with other treatments. There needs to be more scientific research, experiences, and training.

Not true: There are many proven natural treatments/cures that we recommend for treatment of certain conditions. List includes calcium, vit d, fish oil, ginger, oats, digoxin, vit b3 (niacin), some statins (eg lovastatin), many many others. One common philosphy is to favor treatments proven to be effective, to disfavor treatments proven ineffective or dangerous, and to be cautious with unproven treatments.

They do all the time: If you have taken an antibiotic, chances are it is a derivative of a natural product produced by a fungus: penicillium. You are of course assuming that natural is good, forgetting that natural is a mixed bag. For example smoking the natural product tobacco is a leading cause of death. There are a lot of claims about natural remedies, almost all of them are never proven or proven wrong.