My first reason is that they live longer. It has been scientifically proven that most animals live longer in captivity. The average wild turkey vulture lives to be nine years old. The average turkey vulture in captivity lives to be 12 years old. That just proves that captivity is better for most animals.
My second reason is to save endangered animals. When you put an animal in a zoo it eradicates all risks of them getting eaten by other animals or hunted by humans. The rhino is also endangered because it is hunted for its tusks. When you put a rhino in a zoo