I think it's partially the ingredients. The amount of added sugar has skyrocketed. Also portion sizes have become so large, and what we get in restaurants influences how much we serve ourselves at home.
I found this great article that shows the USDA illustrated guidelines starting from the early 1900s. In 1956, people were told 2 servings milk, 2 servings meat/egg/beans, 4 servings of veg and fruit, and 4 servings of bread/cereal. I can picture those amounts in my head and it feels reasonable. By 1992, we were being told a minimum of 6 bread and 5 veg/fruit, with upper limits provided that would make it "okay" to have 11 bread, 9 veg/fruit, 3 milk, and 3 meat/bean. If you assume 3 meals per day and take the upper limits, just imagine having 3-4 bread/grains, plus 3 veg/fruits, plus 1 meat, and 1 milk for every meal, every single day! And the government experts are telling you that's a great idea!