As you say, Apple could roll that to their desktop multiuser environment (who has or wants a multiuser phone?) and quickly have something disruptive in the education/corporate space. But although they pushed hard on that market with OSX server it never really took off and got buried. Seems like the profit is in consumers and their vanity shiny toys.
You're a bit behind the times, one has been able to do this for ages on macOS. You can selectively store all sorts of data automatically synced to iCloud, from the contents of your home directory, browser bookmarks, contacts, passwords, calendar, email, photos etc. through to data from apps with specific iCloud support baked in. Relevant bits are even shared with associated iPhones and iPads automatically. Anything signed in with your apple id has access to it. If you took the fullest set of options you could switch to a new Mac (or a freshly minted local account on someone else's Mac), sync all your stuff from iCloud and have a machine set up exactly like your other(s) in the time it took for the sync to happen.
The erstwhile server version of OS X provided much the same facilities, but not quite so extensive. The principal difference is that the OS X server based version used mostly open interfaces so it was easy to divert some services to platforms other than OS X (i.e. one might choose to store home directories on an NFS server) and there was OKish management tools to allow you to do this. You could even cobble together a set-up that looked to an OS X client as if it was OS X server, but was actually provided entirely on Linux, BSD, Solaris or whatever you chose, even down to the directory service that glued it all together. In fact that was how I previously had home set up - you could take a brand new Mac out of the box, plug it into the network, option click at login, and have it copy all one's settings, home directory and preferences onto the new machine and then keep it all in sync henceforth automatically. iCloud is really just a smoother, more all-encompassing version of that.
Those older interfaces are still mostly there if you know how to use them, but they aren't promoted the way they used to be. Facilities introduced for iCloud since the demise of OS X server are difficult or impossible to divert to infrastructure of one's own choosing which is a pity when compared with the old way of doing it.
Most importantly, you can still choose to use none of this and have your macOS computer sitting in glorious isolation, with no need for an apple id, iCloud or any of that stuff and still be able to make full use of it. The only thing you'd lose is tight automatic integration with iPhones and iPads, but you wouldn't lose
all integration with iPhones and iPads, it would just be a bit muted and more manual.