A demand for the average American to eat more meat would have to explain, as a baseline, why our already positive trend in meat consumption isn't yielding positive outcomes. There are potential explanations (you could argue increased processing offsets the purported benefits, for example), but those are left unstated by the website.
[1]: https://www.agweb.com/opinion/drivers-u-s-capita-meat-consum...
[2]: https://ers.usda.gov/data-products/chart-gallery/chart-detai...
Also, you need to adjust for demographics. In 1900, 35% of the population was under 15: https://demographicchartbook.com/index.php/chapter-5-age-and.... Today it’s only 19%. Children and babies obviously eat a lot less meat than adults, and they make up a much smaller share of the population today than back then.