With recent OS versions they’ve actually been rearchitecting a lot, all the way from the kernel to user space frameworks to enable those changes and down to thi

With recent OS versions they’ve actually been rearchitecting a lot, all the way from the kernel to user space frameworks to enable those changes and down to things like their bootloaders. See DriverKit and ExtensionKit for some examples but there’s been several analysis of the OS updates each year. I assume that’ll settle with time because you’re right that it’s not something that should be often. However that only applies to single code paths. The OS upgrades different things each year so it becomes frequent if you account for everything. As for delays for older systems, that is unfortunate. It’s likely just a resourcing issue with all hands trying to get the newest OS to be stable since the goal is to keep users moving forward to architecturally more modern OS versions . The security patches for older systems are therefore a crutch till they can get those users onto the newer OS.