Pepsi does not disclose a specific reason for the change. It is probably just for marketing, and to keep their look "fresh"
Food and drink
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells in an effort to produce energy, maintain life, or stimulate growth.
Historically, people secured food through two methods: hunting and gathering, and agriculture. Today, most of the food energy consumed by the world population is supplied by the food industry.
Pepsi One, corporately styled Pepsi ONE (so named because it contains one calorie per eight-fluid ounce [230 ml] serving), is a sugar-free cola, marketed by PepsiCo in the United States as an alternative to regular Pepsi and Diet Pepsi.
The Pepsi Challenge has been an ongoing marketing promotion run by PepsiCo since 1975. It is also the name of a cross country ski race at Giant's Ridge Ski Area in Biwabik, Minnesota, an event sponsored by Pepsi.
The challenge originally took the form of a taste test. At malls, shopping centers and other public locations, a Pepsi representative sets up a table with two blank cups: one containing Pepsi and one with Coca-Cola. Shoppers are encouraged to taste both colas, and then select which drink they prefer. Then the representative reveals the two bottles so the taster can see whether they preferred Coke or Pepsi. The results of the test leaned toward a consensus that Pepsi was preferred by more Americans.