Humans are the most effective predators ever. If we don't actively protect all "large" animals, we will just murder them all with our lifestyle. By accident.
Now, how do we get people to care about all these wonderful creatures?
My answer is that we make sure that all humans respect and expect to care for animals. That means that children need to see these animals.
To me, that's a zoo. Yes, that's enslaving the animals, but seeing an elephant makes me much more likely to give two shits about keeping it alive.
The problem with this attitude is my kids already love elephants and hate zoos.
My daughter cried the first time she saw an elephant at the zoo, and asked me why they were all in cages.
She called it an animal prison and I kinda agree.
The younger generation gets plenty of world information from the internet now, they don’t seem to need or like the idea of zoos like we did growing up, before you could just see any animal any time you wanted with a pocket computer.
I grew up near a zoo that's pretty big and tends to take really good care of the animals. Some exhibits, especially those in the newer Africa section, don't even have any obvious fences because the cages were designed with natural walls. The result was that while they had some older exhibits that felt like jails, those were being phased out in favor of the more natural ones.
When I got older I was surprised to find out that exhibits like that weren't normal. It wasn't normal for the tigers to have 2-3 acres of land, with visitors viewing the tigers from bridges. It wasn't normal for the ostriches, elephants, zebras and giraffes to share a massive exhibit covering a quarter of the park.
What was normal, was putting them in tiny boxes.
What the fuck?
However, it is because of my experiences growing up that I believe zoos can be ethically created and maintained. The issue is that they need a lot of space and funding to do so, which they rarely get.
They need that much land in the wild because they're apex predators, and that's the amount of land necessary to support enough wildlife to feed them continuously. Not because anything less than that is confinement to them.
My cat just decided to move into my house one day. That was that. She doesn't like when I play videos on my ipad with the sound on. I don't do it without headphones anymore. She doesn't like when I cook spicy foods, I installed a kitchen door and a window fan to keep the smells out of the rest of the house. She doesn't like when the blinds are all the way down and she can't see outside. They are never less than 6 inches from the window sill. She doesn't like it when I eat without sharing, I always have plain chicken to put on my plate to give to her. I'm pretty sure I am the one who has been domesticated.
Arbitrary reasons. All the reasons people gave you are abritrary and I am sorry no one here told you the brutally honest truth. Cows are slaughtered by the millions in one country but are sacred and protected in another. It is all justifications humans come up with so we can live with our choices.