Here's industry reports
https://www.nationalbeefwire.com/doctors-group-applauds-comm...
https://www.wattagnet.com/business-markets/policy-legislatio...
And straight up lobbying groups
https://www.nationalchickencouncil.org/new-dietary-guideline...
https://www.meatinstitute.org/press/recommend-prioritizing-p...
Lobbying groups, putting out press releases, claiming victory...
Here's some things you won't find in any of the documents, including the PDFs at the bottom: community gardens, local food, farmers markets, grass fed, free range... Because agribusiness doesn't make money with those.
Just because you might like the results doesn't mean they aren't corrupt as hell
I have not seen the pyramid with bread, cereal, rice and pasta at the base pushed for at least ~20 years. Maybe it was 25-30 years ago when I saw it pushed seriously in school and even then I did not see people taking it seriously outside of those lessons, as in people actively calling it questionable.
the first one was in 1982 or something, so you have nearly 3 whole generations who were exposed to it (X, Millennial, and Z). I really can't tell if you're actually incredulous; because all the nutrition stuff is told to schoolchildren. Adults don't use a chart, they use self-help books.
The first one came out in 1992, and was active until MyPyramid came out in 2005. Which was then active until MyPlate came out in 2011.