They aren't all that scared of a small subset of geeks running Linux directly on their iPad and using that as a regular Linux-ey thing, I don't think. The number of people who want to do this is very small, and they don't expect any support for that. And that's not possible from the app store, anyway.
But they've always been scared of emulators in the IOS app stores, and the reason for that seems to be a combination of things:
1. The user experience with emulators can be awful, which is a contrast to the "It Just Works" way of doing things with IOS. This doesn't jive with the image they sell, or that they wish to support.
2. By letting anyone run real software easily on an iPad, this cuts into their sales of MacBooks. This is obviously not in their interest, since they'd rather sell two machines instead of one machine.
For point 1 I'm not sure how may people are going to fire up Window on an emulator, find it doesn't handle touch events very well, and go "iPads suck". However, there are a number of people who have gone "I'd like to do X on the iPad but there's no good way to do it, iPads suck", especially in the developer realm.
This is especially true on the "Pro" version of the iPad, where the OS feels like a major constraint on what would otherwise be a very capable device.
You don't need to touch your Windows VM. The iPad Magic Keyboard cases have trackpads on them; and iPads also support Bluetooth mice.
(And a user of iPadOS VM software probably wouldn't even be trying to touch the screen to interact with the software anyway. After all, why boot up such software if not for productivity? And who would attempt productivity on an iPad without putting it into its "productivity orientation", with the iPad docked onto a keyboard case?)
You forgot #3: By letting anyone run mouse software on iPad, they have to use a stylus to operate it, which made Steve Jobs mad at Microsoft's pen computing division back in 2001.
I honestly believe this to be way more important of a reason to Apple than anything else. The point of making you buy two computers is not to get twice as much money out of you, it's to get app developers to port their apps over to UIKit and make you re-buy all your apps twice.
I tried UTM SE a while back. Using it with the Magic Keyboard was almost the Real Deal Laptop Experience, but if I ever took my iPad out of its Magic Keyboard then I'd have to use some really annoying mouse and keyboard emulation to use the same software. Apple's the kind of company that will absolutely put guns to the heads of their users to force them to not have a bad computing experience.
> They aren't all that scared of a small subset of geeks running Linux directly on their iPad and using that as a regular Linux-ey thing, I don't think.
I don't think they are worried about a few geeks running bash or docker. They should worry about Valve Software, and millions of non-geeks discovering that Steam works on iPads. Even if only a small subset of the Steam library works, that could be a collection of thousands of games going back decades that don't pay the App Store tax.
Unfettered PC emulation threatens billions of dollars of Apple revenue.
1) Things don't "Just Work" with IOS. I regularly have to help people figure out how to connect their i* to work network, install 2FA apps, find missing 2FA notifications, find freshly installed app icons..."It Just Works" if you have done it 100s of times before and know what to do.
2) That is just plain and simple user hostile behavior that is not tolerated in case of any other company except Apple by Apple users.
1. I don't have any trouble with IOS. My experience is very limited: I've got an old iPad Pro that runs the current IOS, and that I've had for a couple of years. It Just Works* -- it lets me watch dumb shit on YouTube, check the weather, and remotely operate a digital mixer, and that's all I really want from it. Previously, with a gap of about a decade, I had a minty-fresh OG iPod Touch that also Just Worked* (until it died a couple of years later during battery replacement surgery). Despite my limited experience, in both cases I've found the interface to be adequately intuitive and don't recall ever really seeking any guidance.
2. Some people like the walled garden. I'm not really amongst them, but I do tolerate the walls. (For those who absolutely abhor walls, there's rootable Android devices out there that can satisfy an itch to tinker with something in compact portable electronics. That's a lot of fun, too, but it's heading in the opposite opposite direction of Just Works.)
*: They "just work" within their limitations, which can be severe. It frustrates me that I can't install real Firefox on the iPad so I can use uBlock Origin, and it frustrated me that the iPod Touch didn't even come with the ability to install apps or even copy-and-paste text out of the box**. But in both cases, the devices behaved very well with the functions they were permitted to utilize.
**: I jailbroke the iPod Touch and went pretty far off the reservation with it (adding a clipboard, installable apps, multitasking, and a useful userland) because that was fun for me at that time, but by no means did I have to do any of that -- it was a very fine touchscreen music player with 802.11 and a web browser all by itself without any of that kind of help, and that's pretty much what it was promised to be able to do. And that was a long time ago; during the gap, I'd forgotten more about IOS than I ever knew.
3. It lets users get software on to the ipad without going through the App Store (thereby escaping apples ability to clip the ticket on the way through).
But they've always been scared of emulators in the IOS app stores, and the reason for that seems to be a combination of things:
1. The user experience with emulators can be awful, which is a contrast to the "It Just Works" way of doing things with IOS. This doesn't jive with the image they sell, or that they wish to support.
2. By letting anyone run real software easily on an iPad, this cuts into their sales of MacBooks. This is obviously not in their interest, since they'd rather sell two machines instead of one machine.