I finally figured it out. It’s because scientists have not officially blessed its use. To take a drug that scientists say you shouldn’t try yet is to commit a horrible transgression against the authority of the scientific clergy. Even when you’re dying of stage 4 cancer and no scientifically sanctified therapies are available you are not allowed to wander off the reservation and try unsanctified remedies. You should instead just die quietly without making any waves.
Disclaimer: I am not affiliated in any way with the above sites. I have no financial interest in DCA. I have no friends or family suffering from cancer who stand to benefit from DCA.