Maybe people like cats but don't want it out murdering all the local wildlife?
This too. Also the risk of injury from other cats, and other animals.
Bella tried to take down a seagull once - even on her harness - and the thing was twice as big as her!
I mentioned our man-made environment being an alien one for cats - well also the cat density here is completely unnatural. Without humans there would be fewer cats and more cat predators.
Really, cats today can't be seen as wild animals, or animals that should "roam free". Because we need to realise that mostly our urban environments are not natural, to varying degrees not safe, and actually quite stressful for many cats. Second, they are domesticated.
Some do in fact prefer the quiet, indoor life to the man-made urban jungle. I know Bella does. She has the opportunity to go outside multiple times a day, and prefers mostly just a very quick sniff and circuit of the garden, then straight back inside.
Maybe I've conditioned that into her, maybe it's what she would choose for herself, ultimately it's not very exciting but it's safe and she's well provided for. No issues with fleas or fights or getting run over or the like.
Not saying it's the only way but it works for us. Keeping her occupied
is a struggle tho. I think she does suffer a bit from boredom. And that does play on my mind.