It's like the plot of Dallas Buyers' Club, if any research suggests that something expensive is better then it will be used regardless of how efficacious it is. It's not black and white like a conspiracy and instead varying shades of grey. Vitamin C gave mixed results without toxicity instead of chemotherapy drugs giving mostly positive results with toxicity being a common side effect, so the latter is more medically sound for treating the issue for doctors. You learn pretty quickly that many doctors accept harmful side effects if the issue is treated at the expense of the patients.