Is reinstalling the OS on an iPhone really a thing? I can't imagine that any significant number of people do that. Non-iCloud backups are probably more common but still extremely rare, as are any backup solutions that require more than a few minutes to set up and permanently automate.

For the first part, probably just take it to the Apple store or just "factory reset" it. I don't think the average apple user cares enough to completely reinstall iOS themselves. Same goes for non-iCloud backups - the average person probably doesn't care enough to do backups normally, much less plug it into their computer manually. I'm not saying you're wrong, but rather taking your complaint with a grain of salt. It's sad but the average apple user (from my experience) doesn't care.

I can't think of a time I've wanted to reinstall the OS. I've wanted on several occasions to factory wipe the device (trading in the phone, fresh start, repurposing it, etc), but "Reset all content and settings" is an option locally on the device.

As far as backups: as a matter of general data hygiene I don't let my iPhone or my laptop be the source-of-truth for anything. Contacts sync to iCloud and Google, Photos to Google and Dropbox, etc etc.