My wild guess before reading the article: unhealthy food. A big part of which is herbicides and pesticides. I will now read the article.
Don't people eat more healthy than they did 50 years ago? Weren't microwave dinners a big thing in the 70s?
One example: long ago I used to buy Bush's baked beans in a can. They had a vegetarian version which I assumed was healthier, and it even tasted better than the original. But one day I compared the labels and found the vegetarian version had more added sugar and more calories per serving.
We were fed a massive amount of misinformation about healthy foods in the 1980s. Hopefully things will improve from now on.