The result of misguidance from health professionals, big food & big pharma marketing.
Not acknowledging that health is largely a result of lifestyle choices, and that pharmaceuticals are mostly ineffective and often harmful.
And now for the specifics:
- lies/bad science about meat (particularly red meat) being unhealthy
- lies/bad science about cholesterol & saturated fat being unhealthy
- not attacking sugar and processed foods at the highest level; should be treated like smoking if not even more harshly
I say this for experience, until I fell ill I had no idea about either of those things. Like many of my peers, grew up with tons of sugar, and many misconceptions about what is healthy (although thankfully to a lesser extent than what's common nowadays)
I'd also add that these things compound over the generations. We are more sensitive than our parents. It checks out for me, every generation has worsening autoimmune symptoms.