Automatic updates, single stop and little worry for malware are all perfectly achievable without a walled garden. It's been a thing on Linux for ages. It even gives you the choice of how high you want your walls, whether you only trust the debian developers or a user-made aur package or anything in-between.

Perfectly achievable, at the expense of being an end user nightmare.

The reason I'm buying an iPhone is I don't have the time to care about how high the walls should be and to ensure every app I use isn't abusing the SDK to suck up data. The reason I'm paying a premium for Apple is I'm choosing to trust them rather than trust every developer.

The day apple, microsoft or google would manage updates of a whole system as well as some linux distribution would actually be the end of many user nightmares.

Unless you don't install any app, you still trust all the developers of the apps you install. Walled garden is just a nice way to name Authoritarianism applied to a platform.

It might make you feel safe to have apple deciding every bits of what you can do with your phone but it does mean that: - it's secure - the apps you are using are - you still have very low control over your data.

You just pay to close your eyes and feel safe.

That’s true of all closed source software, not just walled gardens. Any time you don’t have the source, you’re trusting that the developer isn’t screwing you over.

I’d rather trust Apple than the cumulative two dozen developers that have their software running on my phone.

Or to put it another way, Apple provides systems administrator services with every phone. Most medium and large businesses pay a LOT of money for systems administration to ensure that their desktops and laptops work reliably.

And yet the only way it was successful on the mainstream was via ChromeOS and Android, which hide from userspace that they are even using the Linux kernel.

You are confusing "because of" with "in spite of"

Where is the evidence that any of that was required?

Apparently yes, given the amount of "Linux" developers that rather pay Apple for a UNIX desktop experience instead of making "Year of Desktop Linux" actually turn into a reality beyond the usual 2% from Steam surveys.