Have you used Android? Has it ever failed an update or break due to an app install in a way that can’t be fixed by uninstalling or factory resetting it? Android is an immutable Linux OS. Its system files are stored on a read-only partition. They’re only mounted read-write during update. (That’s a lie, this is no longer the case, but it used to be.) Apps are also stored in read-only form. One implication of this is that upon update, the partition/files you want to update are always in a predictable, unchanged state. That guarantees successful updates. It also allows trivial diff updates. The other implication of these facts is that you can always delete the mutable part of the OS, where your data and the apps’ data is stored, and you’ll always end up with a clean, working OS in a factory state. On Android you can also do this per-app by tapping “Clear data”.