Well you can thank Big Pharma that you cannot easily get Cannibis oil which is curing cancer right and left.
Ah, and the mythology of cannabis grows.
There is no proof that cannabis does anything curative, but plenty of proof that it is harmful. There is, furthermore, reason to think that marijuana is a carcinogen.
All of the scientific evidence doesn't matter: with marijuana, the push is for use based on anecdotal rumors. That's not the way drugs should be included in the pharmacopeia!
BTW, there is a marijuana oil (THC) extract that is prescribed and sold. It is, of course, packaged, quality checked, and sold by pharmaceutical companies.