As with all information, society as a whole "owns" macOS - Apple only has been granted a temporary monopoly of this information in order to encourage them to create more.
Innumerable court cases have turned on what are often negligible practical differences. Apple is said, legally, to "hold" copyright. Saying they "own" it would mean they have all sorts of rights and powers around it that we as a society choose not to grant to them.
That is not to say that numerous judges have not, on their own initiative, elected to grant holders many such powers. Judges can be just as confused as anyone, and more than some, and so exceed their statutory authority. Congress, moreso. But there is still a difference.
Sure, and I didn’t argue for or against the use of that term. The legal definition of theft varies by jurisdiction, but is not necessarily limited to physical objects (e.g. services). I have no idea whether it’s appropriate in this case (I’m not a lawyer), but feels more like copyright infringement.
Control is a part of ownership. If you don't control how something is used and by whom, you don't really own it. So either using it in unauthorized ways is in a manner theft, or Apple's "ownership" is not real ownership. I'm not sure what the solution is, but IP is a tricky concept no matter your position.
It has nothing to do with actually preventing all infringement, but instead seeking enforcement in at least some cases. If a copyright owner is aware of substantial infringement and chooses not to pursue (or license) they may lose their copyright through genericization or other means.
(Caveat: I’m not a lawyer, but I learned broadly the above from an IP lawyer.)
