Well yeah cause the parrot has everything it needs within a few feet of it at all times.My only experience with bird owners have been people like my parents that owned parrots. I've never seen a full time caged parrot but they really seem to prefer sitting on top of their cages as opposed to wondering around too much. It's kinda like they recognize that their cage is their "home" and seem to feel safe there.
One time our parrot got outside somehow and immediately started waddling back to the door like it was going "nope nope nope". Definitely didn't like being outside.
The thing with parrots though is that they need lots and lots of attention and affection to be at their best. It's a very demanding time commitment.
Absolutely no clue about smaller birds.
I think people are missing the point of why birds fly so much; they have to do things like migration and fly around hunting for food for survival. If a human is providing food, all season shelter, and companionship...the bird really doesn't need to fly very far.
Wing clipping and having a bird always caged seems pretty cruel to me, but otherwise I think responsible, caring bird ownership is probably fine.