I think a lot of it stems from the commodification of healthcare and an overall distrust of institutions. "They" just want you to get sick so that you can be given prescriptions etc. Which getting a general vibe of American capitalism isn't particularly sensationist, they can see that basically everything falls under the profit motive but aren't able to articulate why other than we're seen as disposable. This likely becomes more acute with age as people see friends/family abused and disregarded by health providers, and our monkey brains fall back on "Well there must be something I can do so this doesn't happen to me and I can't pronounce words with more than two syllables and things I don't understand scare me."

A lot of the organic fanaticism also comes out of the same vein, that most farmers are dousing everything with synthetic pesticides and are either ignorant or malicious with their use. Obviously if I can pronounce organic pesticides like boron or copper sulfate that means they're not bad for you and definitely don't bioaccumulate or cause brain and organ damage when ingested regularly (most people assume organic produce has no pesticides and that's why its more expensive).