Most Helpful Girl
It's tradition. They've been around since ancient Rome, and, if you can believe it, the people who liked to watch humans kill each other in hand to hand combat weren't exactly known for their humanitarianism. For people in the more recent past, circuses were the only chance they had to see exotic animals. Today, I think most people consider them antiquated and barbaric. I wound't be surprised if circuses died out completely within the next 100 years.
Most Helpful Guy
variety is stimulation. its a different form of entertainment, where people can see animals in many different ways.