..because we love to get entertained.
Vegans are by no means concerned only on food because veganism means not only to stop consuming meat, fish, poultry, dairy products, and eggs, it rejects the repression and imprisonment of naturally free creatures for any reason.

Entertainment: Reject Circuses, Zoos, the use of Animal as Actors…
Chapter 2: Suffering just for the fun of it
Mainly for the purpose of our own amusement, over thousand species of animals are imprisoned in zoos all over the world. Zoo animals are captured from their natural habitats, bred in breeding-programs, or purchased from other zoos. Many of them were forced to travel long distances within small cages. Some of them arrive ill, injured, or death. Even in zoos with so-called natural habitats surrounded by electric fancing, water ditches, or concrete walls, animals have to spend most of their lives in hidden housing areas, which are nothing more than cages. In every zoo, animals exhibiting neurotic, stress-induced behaviors like weaving forth and back or throwing items towards humans can be found. The difficulties that zoos have to get certain species to reproduce is also an expression of stress preventing animals from engaging in normal sex and childbearing behavior. A result of extensive breeding-programs to provide continuous animal babies as visitor attractions is that the surplus of animals, particularly the elder ones, have to be sold to other zoos, laboratories, and private exotic-animal collectors. In some cases it is also common to use these excess-animals as pet food. Furthermore, zoo employees and veterinarians are often not well trained to handle the broad range of species and exotic animals adequately.
Regardless of that facts, zoos are often defended on the ground that they provide education about animals to the public. The truth is that confined animals teach us little about what they really are and only a minor percentage of zoo visitors spend time to read the provided informations, if any are given. Zoos rather increase the gap between non-human animals and us as the “self-declared” superior specie.
In summary, zoos are nothing else but companies engaged in the capture, incarceration, and breeding of animals to exhibit them like things for entertainment purposes.
If it is wrong to inflict unnecessary pain and suffering on sentient beings for sheer amusement, then we have a moral and legal obligation to oppose the imprisonation of animals.

It is up to you.