Why isn't this treatment better promoted and made available to all cancer patients?"

There is no credible evidence to show that Gc-MAF can rebuild the immune system or eradicate early stage cancer. Many scientists are trying to train the immune system to destroy cancer cells. Gc-MAF is supposed to work along similar lines, but it has not been proven. 

The immune system is meant to seek and destroy viruses, bacteria and tumour cells. Gc-MAF is part of this system – it recruits a type of immune cell called macrophages that suck up infectious cells. However, tumours produce an enzyme called Nagalase that prevents the body from making Gc-MAF. This helps them to evade macrophages. 

American scientist Nobuto Yamamato has published three papers that apparently show how small amounts of Gc-MAF can “cure” people of breast, bowel and prostate cancer. However, it is not possible to prove that from Yamamoto’s studies because of problems in the way the studies were conducted (two of the three papers have since been retracted by the journals they were published in). These issues are outlined in Cancer Research UK’s Science Update blog. Without more rigorous research, it is impossible to say whether Gc-MAF has any effect at all, much less if it can cure cancer.