"to give ballerinas a light, airy look, making look as if they are floating when they move across the stage" as taken from the following article found at http://www.ringsurf.com/online/2182-two_types_of_tutu_a_history.html "Though the first tutu was merely a skirt cut just above the ankles to reveal a dancer’s feet, these skirts eventually migrated north. As ballet became more and more popular two types of tutu emerged: the long romantic version (or Juliet style tutu) and the shorter, more provocative style (now often called the Classic tutu). The first romantic tutu is often attributed to the famous virtuoso ballerina Marie Taglioni. In 1800s Taglioni became known as the first ballerina to dance “en pointe” (on her tip-toes in ballet slippers). The tutus worn by Taglioni were often cut to below the knee to reveal the intricacies of her famous legwork. These romantic tutus were delicate, feminine and were made of material that allowed Taglioni to move about freely floating through the air and executing the precise movements that gave her cult status. The to this day the romantic tutu is still made to be long and flowing, giving the ballerina a weightless, ethereal appearance. As ballet continued to become more popular connoisseurs of the art form demanded to see more when it came to the intricate dance movements that dancers performed. Again the tutu shrank. The style of tutu commonly referred to as “classic” is a short, stiff skirt that juts out horizontally from a ballerina’s hipbones exposing her legs entirely. The classic tutu is often worn with a leotard, which hugs the dancers body. Both romantic and classic tutus are designed to give ballerinas a light, airy look, making look as if they are floating when they move across the stage. Although the tutu has evolved significantly, tutus today still serve the same purpose as those designed two hundred years ago."

Because they look silly on truck drivers :)