I'm not going to comment on the health merits of the pyramid because I am not a dietician. However, I can speak to its development as public policy. Note that I am writing specifically about the development of USDA dietary recommendations, and only through the adoption of the pyramid in 1992, which is no longer USDA policy.

The earliest "food guides" were published by the US Department of Agriculture in 1916 and 1917 to translate the dietary recommendations of research scientists into specific food recommendations. "How to Select Foods" was written by USDA nutritionists Caroline Hunt and Helen Atwater as a guide for how homemakers should feed their families. Foods were categorized into five groups: milk and meat, bread and cereals, vegetables and fruits, butter and fats, and sweets, with the recommendation that each meal include something from each group. The goal was to inform people how to feasibly apply nutritional recommendations given food availability and costs, as well as existing consumption practices (Hunt and Atwater, 1917). There's no evidence of any sort of industry involvement here -- the guides took the research of W.O. Atwater, who was the "Father of American Nutrition" (and also Helen Atwater's father) with an emphasis on ensuring adequate nutrition. It's important to note that the dominant public health concern at the time was malnutrition.

In 1941, FDR convened the "National Nutrition Conference for Defense" which brought 900 delegates to DC to develop recommendations for a national nutrition policy. The delegates were mainly health and science types (doctors, chemists, nutrition researchers, leaders in home economics) but people from agriculture, labor, industry, consumer groups, social services, and government agencies were involved as well (National Nutrition Conference, 1941). This leads to the first Recommended Dietary Allowances for calorie and nutrient intake and the USDA's Basic Seven food guide in 1943 (USDA, 1943). In 1956, this was simplified into the Basic Four, which recommended daily intake of fruits and vegetables, milk, meat, and bread/cereal. This is a "foundation diet" in which the goal is to tell people what they should eat to meet baseline nutritional needs, which they then supplement with whatever else they want to eat, including sugars, fats, and refined carbs. Industry representatives were invited to review the Basic Four and were generally supportive as the guidelines were basically "eat more!" (USDA, 1956).

That's a highly simplified version of the early history, but it's important because throughout the evolution of USDA food guides, there's an emphasis on considering what people are used to eating and what foods they have access to in addition to what the current science says about required nutrients. Recommending modifications to the diet people are accustomed is assumed to be more effective than telling people to completely revamp their diets. So the Basic Four is the starting point for the discussions of the 70s and 80s that eventually lead to the adoption of the pyramid in 1992.

In the 1970s, there was a shift away from concerns about nutrient deficiencies to overconsumption, as research linked too much fat, sugar, and salt to various health conditions. The US Senate Select Committee on Nutrition held hearings and issued a report recommending increased carbohydrate intake, and decreased intake of fat (especially saturated fat), cholesterol, sugar, and salt (Select Committee on Nutrition, 1977). The meat, dairy, and egg producers were upset and requested additional hearings, where they put forward several scientists who told the committee there wasn't solid proof of a link between diet and heart disease. The combination of industry pressure and apparent disagreement in the scientific community led to the committee issuing a revised version of the report (Oppenheimer and Benrubi, 2014). The most notable change was that the recommendation to "decrease consumption of meat and increase consumption of poultry and fish" became a recommendation to "decrease consumption of animal fat, and choose meats, poultry, and fish which will reduce saturated fat intake" (Nestle, 1993).