Why does pepsi advertise and change so much?

Pepsi advertises so much to keep in the public domain and to keep the brand noticeable. Pepsi's main reason for advertising is to keep people aware of the brand and products. They don't want people to forget about the brand and purchase other leading brands instead of their own. Pepsi use celebrity's to grow their sales in big budget commercials and adverts. They play on whos admired and tendy at the time.