I'm supporting three people, only one of them lives with me. My parents live in a different city, pretty far away (far enough that just randomly visiting them for in-person troubleshooting is not an option). I maintain three separate computers for them. It doesn't take much effort nowadays, because I used a system I am familiar with, a general purpose distribution, and set it up so that I can manage it remotely.
I wouldn't be able to maintain a more limited system for them, because it would lack the tools I need for remote maintenance. Hence my assertion that distributions focused entirely on non-enthusiasts are a futile attempt.
It's not even the upgrades. Automatic, unattended upgrades have been a thing for a long while, and in general, they work remarkably well. At least in the sense that nothing "breaks": programs will still work, and start up, and all that.
But automatic upgrades can change things. Change an icon, move things around, change behaviour, introduce new features, new bugs, and so on. That is the hard part of maintenance, not the technical "go from version A.B to A.C".
Most immutable distros I've seen aim at improving the A.B->A.C upgrade scenario. They do very little, if anything at all, to keep the system familiar. Because they can't, unless they control the entire stack. And even if they do, like in the case of the proposed GNOME OS, the UI still changes - often considerably - between major versions. If I maintain a system for others, I can prepare them in advance. If they do it themselves, they do not have that luxury, they're not going to follow the development of the software they use, and I wouldn't expect them to do so either. I can do it, and I am doing it, because I'd be doing it anyway for myself.