Because birds don't give a fuck about private property. They perch wherever the fuck they want. Some birds are apparently as "intelligent" as children, but I think they're actually way smarter than the bourgeoisie specifically because private property and national borders are all meaningless to them. The entire natural world is anarcho-communist and even Homo sapiens was like this for 95% of our time on Earth.
"No, actually you're wrong because birds have territories they defend and therefore capitalism is natural and we should all embrace it."
Really? Do birds enslave other birds to make money? Do they ever eat more food than they need? I don't fucking think so.
Also, birds are complex. Some are loners. Others hang out together. Sometimes different species even hang out together.
There are also far more bird species on Earth than there are mammal species. In some ways the reign of the dinosaurs never really ended.
When I lived in the American puppet state of "South Korea" I remember hearing about the wildlife in the DMZ and how certain birds there would fly back and forth between the DPRK and the "ROK" because they didn't give a fuck about the border. Based fucking birds.
Also, sometimes I saw spoonbills in the "ROK." That was really cool.
Right now there's a bunch of bluejays freaking out about something just outside my house. They get super active when it rains for some reason. That's why I'm writing this.
I completely understand where you're coming from. I've visited some similar places. One place in Costa Rica had a toucan whose beak was largely broken so I understood why it was there. Some housed birds though absolutely break my heart. Fortunately, I know of some zoos/aquariums/wildlife centers that only house birds they're actively rehabilitating due to injury, and will only keep them permanently if their injury is so severe they'd otherwise die in the wild. But these places have always rubbed me the wrong way because so many species of birds travel such enormous distances, even some every day. For me it just depends on how well their enclosure is and why they're there to begin with.