You're asking this question as if you think animals are the same as us. They're not. When a cheetahs cubs get killed, she'll walk around calling for about 3 days and then get on with life without a matter. How long would you be upset if your 2 year old son got murdered today? A zebra stallion will kick and bite his baby daughter to pieces if her mother dies. He does so to protect his herd. Would we do that?
If you were in a zoo in a cage you would probably always think about trying to escape. Just about all animals in zoo's today are capable of escaping from their enclosures,so why don't they?
Because they establish it as their territory,they get fed there and they get looked after there. They don't think like you and me,so they don't need to have the same rights. They are there to enjoy,learn from,to take care of us on this planet and for us to utilise,simple.
Hope this helps