Because these people know how to spin their "treatment". They convince the patient to chose their "treatment" them selves. They rarely give the ridiculous advice directly in front of witnesses. Instead the family will learn about the treatment from some third party, potentially the victim themselves.
I'm at a hotel that coincidentally has 500 people from a MLM finale/training for Essential Oils and this is what it's all about. Have the people tell their friends and family that the oils can even cure ebola to get your 4 to become 8, 8 to become 16, etc. My SO the oncologist-in-training is pissed that they can just say whatever and aggressively advertise their wares and she can't even get pens from pharma companies.