That's because computing is a new thing in human history. There isn't anything quite like it. But there is matter, and matter is sold with lots of disparate bits built into one product all the time. Things which could be reconfigured by a skilled person, but it's widely accepted that people don't/can't/shouldn't do that.
Your arguments are similarly broken. You can mix your iOS device with any pair of glasses, 3.5mm audio device, wifi AP, or cover, or choose to use only part of it. You can't have a TV dinner without the gravy browning and you can't get an iOS device without the Apple firmware.
The problem is that Apple locks down the platform using digital signatures so that the only way to use anything but an Apple OS or bootloader is to find and exploit a bug in Apple's lockdown code.
And one of the reasons they do that is so they can provide a curated, malware free, beginner-unbreakable, trustable-updating, partly-sandboxed-app experience for their paying customers.
You have complained about my analogies, but you haven't said why "they should" do that, just that "you want them to".
Apple can easily provide the curated experience without locking the device down. Sideloading can be available while still off by default.
The reason Apple has the App Store and restricts distribution channels is to provide a good experience. The reason Apple locks down the platform so hard that the only way even an expert can customize the OS is to exploit bugs is to retain control of the platform, nothing to do with a good experience for users.
As for why they should do it, it's because I want them to, and because I think the walled garden approach is frighteningly dangerous for computing in general. Everybody is following suit. In a couple of decades it's not inconceivable that it will be impossible to publish any software without permission from a big corporation.
It's pretty likely that the moment sideloading is "available but off by default" is the moment phishing messages take off seriously. "Just go to settings, then enable sideloading!". Most people won't know what it means, but will use it if told to.
That's not something I can cite peer reviewed evidence for, but from the number of people with unwanted toolbars and junkware on desktops, it seems likely.
So I disagree that it has "nothing to do with a good experience for users".
the walled garden approach is frighteningly dangerous for computing in general.
It has made something widely regarded as the best non-technical computing experience of the decade. It's not 'frighteningly dangerous' while there are still lots of ways to get computation you want done, done. (Albeit not as slickly).
Sideloaded apps could still be sandboxed. It is the sandboxing which helps against malware, not the App Store approval process (which is not at all thorough and not equipped to detect malware at all).
That's because computing is a new thing in human history. There isn't anything quite like it. But there is matter, and matter is sold with lots of disparate bits built into one product all the time. Things which could be reconfigured by a skilled person, but it's widely accepted that people don't/can't/shouldn't do that.
Your arguments are similarly broken. You can mix your iOS device with any pair of glasses, 3.5mm audio device, wifi AP, or cover, or choose to use only part of it. You can't have a TV dinner without the gravy browning and you can't get an iOS device without the Apple firmware.
The problem is that Apple locks down the platform using digital signatures so that the only way to use anything but an Apple OS or bootloader is to find and exploit a bug in Apple's lockdown code.
And one of the reasons they do that is so they can provide a curated, malware free, beginner-unbreakable, trustable-updating, partly-sandboxed-app experience for their paying customers.
You have complained about my analogies, but you haven't said why "they should" do that, just that "you want them to".