The thing is. We have chickens. Every time there's a new nest, there's a chance multiple roosters hatch. And you can only have one rooster, so we have to sell them. We always try to sell them as pets first, but that's an oversaturated and underwanted market. So usually we give them to a local falconer instead.
We also have two chickens that are unusually mean. Most of our chickens are hand-raised and perfectly lovely, one will even come up to you for hugs. But two of them are mean, will peck at other chickens, peck at us, and even kill chicks. So we had to separate them. The only reason we still kept them around is they laid a lot of eggs, which our other chickens didn't do as much.
However, recently they stopped laying. Personally, I don't mind having a second, smaller aviary for two meaner chickens, but my mother would rather get rid of them as soon as possible. The local falconer won't take adult chickens, but if he did, that's where they'd go.
Most farms (or farm-like houses) will end up with unwanted animals. Rabbits, well, breed like rabbits, and not all owners can take care of that many, and you can't always sell all of them. So giving them to a zoo to be used for food is fine. I can see why people may have a problem with it, but in truth it's no different than giving them cows, pigs, or even fellow zoo animals. The main difference is that people usually see pets more up-close, and won't see them as food