The bands for meat and protein (purple) and oils (yellow) are thinner than the others. That's because the body needs fewer of those kinds of foods than fruits, vegetables, grains, and dairy foods.
The bands start out wider and get thinner as they reach the top. That's designed to show you that not all foods are created equal, even within a healthy food group like fruit. For example, apple pie would be in the thin part of the fruit band because it has a lot of added sugar and fat.