It's because human beings are messy! If you feed a person a peanut, they might think it's tasty. If you feed a different person a peanut that person may die, quickly. If a god damn peanut can illicit that range of responses in a healthy human being, imagine literally anything else. Of course there is corruption because so much money is on the line and humans in aggregate are a selfish bunch. One thing I always like to point out is that people who try to follow the science and the latest guidance aren't the ones speaking in absolutes. I'm aware the CDC or FDA have gotten things wrong in the past and will get things wrong in the future, but it's the best system we have. It's the anti-science people who speak in absolutes but then the second the cancer diagnosis comes in they come running back begging big pharma for treatment, they'll even bankrupt their entire family trying to get that treatment. It can't be both ways. This is why it's hard to take skeptics seriously. Not only do they throw a thousand things out there, and maybe one or two is right, they conveniently ignore the other 998 things they got way wrong, but when push comes to shove, they love big pharma and beg for it's treatments.