The Food Pyramid actually misrepresented a balanced diet, as it was partially influenced by food industry's economic interests. It was replaced with MyPlate in 2011, which was more nutritionally balanced.

Source: Harvard Health

The original USDA Food Pyramid suggested a hierarchy of food groups that didn’t reflect actual health science. Lobbying from meat and dairy industries affected how foods were ranked.

From The corrupt history of the food pyramid:

In his first term, Richard Nixon's government had agreed to sell millions of bushels of grain to the Soviet Union.

Unfortunately, there was a particularly poor growing season which resulted in a spike in the prices of grain. So, to minimise public disquiet, the Department of Agriculture unleashed a suite of policies designed to increase grain production and they worked. Before long there were massive surpluses of grain.

About the same time, Luise Light was in charge of a team responsible for crafting the US dietary guidelines.

This process, unfortunately, was informed both by the unsound science within the dietary goals that came from the select committee, and her masters within the USDA. It seems as though the new dietary guidelines were seen as a vehicle by those within the USDA to deal with their problem of the grain surplus.

In 2011, the USDA introduced MyPlate, a simpler visual guide that focuses on portion sizes and balance: showing how much of your plate should come from fruits, vegetables, grains, and protein.