I've started a draft to your comment 3 times now and it always becomes a "not your cloud, not your data" rant :) But better writers than me have, and continue to, bang that drum so I will not right now.
I could write 100 blog posts about this but let me give you one good example: Years ago when many people still synced their iPhones via cable, you could sync all the major "iLife" apps -- photos, music, contacts, calendar etc. When Apple released Notes.app, it was around the time the iCloud push got really big and more people started using that. To this day, you cannot sync Notes.app via cable. It would be a trivial thing to implement, but it prevents cloud adoption and is so clearly in the "wontfix" category that the only conclusion is that it's intentionally left out. Want your Mac's notes on your iPhone? Get in the iCloud, citizen, and maybe we'll let you.
Bottom line is that if you go back and look at Steve Jobs' 2001 digital hub strategy, the futuristic view was one where the Mac was the ground truth for your data and your apps. You were in charge. You owned the machine, it did what you wanted, and you bought neat peripherals that interfaced with it like mp3 players and cameras.
But today the "digital hub" is the cloud, and the Mac is just another peripheral. Today by default Macs and iPhones need to be "activated" via internet connection to reinstall the OS, and any peripherals you buy (looking at you, fucking HP/Epson shit) will likely force you to create a cloud account which means they own it, not you.
<insert cloud rant here>
Side note: Windows is a worse offender, you need look no further than Windows 11 and its removal of the local account except via extremely technical/hacky means. This is an intentionally malicious push to their ecosystem, and one I hope Apple does not follow (but essentially has on iOS and I won't be surprised if/when macOS follows suit).
PPS. One of the next big pushes here will be passkeys. If they can tightly couple your online services to their devices for authn then the ease and freedom to migrate systems is reduced further, and "knowing" your credentials for an online service means nothing. The cloud provider decides if you get to access it or not.
I think that you're viewing the past through rose-colored glasses a little. Steve Jobs' entire strategy was a headless system with everything in the cloud. It was the entire push for iTools (which then became .Mac, then MobileMe, and finally iCloud) and those were released in 2000. The idea was that you could sign in on any Mac and always have access to your personal info and, at one point, even sign in and see the desktop of any of your machines ("Back to My Mac", a feature I miss every day). It only started as one machine being the "ground truth", as you say, because there had to be one starting point to sync from.
That being said, I'll give you that it might be trivial to sync Notes (one-way, at least) via cable. I believe, based on nothing other than my interpretation of history, that the reason this stopped is not to force cloud adoption but that it's just not that in-demand of a feature. The biggest issue with cable-based syncing is that you have to resolve conflicts manually and the iCloud solution doesn't need that at all. It's not a trivial thing to implement, in my opinion, especially if you have to factor in anyone that has multiple Macs, iPads, or any other device that could potentially sync Notes.
That being said... I'm doing exactly what you're describing in syncing everything to my own cloud on my NAS but at the expense of getting to use the native apps on MacOS and my other devices. I still use the iCloud stuff for backups of data on a specific account but I feel like the reason these things are going to continue to be "wontfix" (you give away your dev-ness) is because the majority of people love the convenience of simple syncing that they don't have to actively think about. Apple also does just enough on the privacy and security front to make it worthwhile for a good chunk of techies too.
The Notes app is at least sync'd through mail, so you don’t have to go through iCloud if you don’t want to. I… uh, host my own IMAP server… so it’s my data, on my server. And yes, I realize that “just host IMAP yourself” is a preposterous thing to recommend to anyone.
Seems like this kind of syncing just barely works, because notes are kind of like emails. Too bad there isn’t a similar ubiquitous personal file sharing service that could be used for your other iCloud stuff. WebDAV might fit the bill if you hammered it into place.
I don’t think syncing by cable is in the cards, even for Notes. You would want a way to resolve conflicts. When you sync stuff like music by cable, there’s always a host and a client device. With Notes, there are just two peers, which may both have edits to a common anscestor. A chunk of WebDAV is just the ability to make changes and handle conflicts (or at least figure out when they happen).
I could write 100 blog posts about this but let me give you one good example: Years ago when many people still synced their iPhones via cable, you could sync all the major "iLife" apps -- photos, music, contacts, calendar etc. When Apple released Notes.app, it was around the time the iCloud push got really big and more people started using that. To this day, you cannot sync Notes.app via cable. It would be a trivial thing to implement, but it prevents cloud adoption and is so clearly in the "wontfix" category that the only conclusion is that it's intentionally left out. Want your Mac's notes on your iPhone? Get in the iCloud, citizen, and maybe we'll let you.
Bottom line is that if you go back and look at Steve Jobs' 2001 digital hub strategy, the futuristic view was one where the Mac was the ground truth for your data and your apps. You were in charge. You owned the machine, it did what you wanted, and you bought neat peripherals that interfaced with it like mp3 players and cameras.
But today the "digital hub" is the cloud, and the Mac is just another peripheral. Today by default Macs and iPhones need to be "activated" via internet connection to reinstall the OS, and any peripherals you buy (looking at you, fucking HP/Epson shit) will likely force you to create a cloud account which means they own it, not you.
<insert cloud rant here>
Side note: Windows is a worse offender, you need look no further than Windows 11 and its removal of the local account except via extremely technical/hacky means. This is an intentionally malicious push to their ecosystem, and one I hope Apple does not follow (but essentially has on iOS and I won't be surprised if/when macOS follows suit).
PPS. One of the next big pushes here will be passkeys. If they can tightly couple your online services to their devices for authn then the ease and freedom to migrate systems is reduced further, and "knowing" your credentials for an online service means nothing. The cloud provider decides if you get to access it or not.