They explain it in the films. Doctors in America can only use pharmaceuticals or surgery to treat cancer.
If a doctor find that, for a fake example, banana peels cure cancer; he can not legally prescribe it. He can only use surgery, chemo-therapy, or approved drugs.
The fight against cancer is fought with one hand tied behind the back !
I am a computer repair guy, not a lawyer or doctor, so I'm sure I explain it awkwardly. But I encourage you to watch the 3 films, they are free and interesting, easy to watch.
The cure for cancer has been known for along time, but it's not patentable (like banana peels can't be patented, for a fake example). Therefore it's not interesting to the corporations.
After you watch the films look up "G Edward Griffin". While Max Gerson was finding vegetables in a certain way can cure cancer, G Edward Griffin was finding a completely different cure called Vitamin B17.
Cancer is curable without drugs or surgery