It comes from a history of using mostly trusted application sources like Debian/Ubuntu package archives with manual review being the norm. And few supply chain attacks.

But both Flatpak and Snap offer this new model from the two biggest desktop players in the Linux world: Red Hat and Canonical.

As the sibling comment said though, being an administrator for your own computer (including a phone) does not mean that you will be running untrusted applications as one: on the contrary, if you assume an administrator role and run an untrusted application, naturally, all bets are off. But even as a power user, I'd love to be able to safely run programs I do not necessarily trust, feeding it only data it needs and no more.

Again, Snap/Flatpak provide this model, but we need to see more application authors take them up to ship their software.

Allowing the owner of the device root access doesn't necessarily break the security model. It just means that the user can grant additional privileges to specific apps the owner has decided to trust. Every other app still has to abide by the restrictions.

The fact that Android complains and tells any app that asks whether the owner actually, you know, owns the device they paid for is an implementation detail.

A Linux distribution that adopts an Android style security model could easily still provide the owner root access while locking down less trusted apps in such a way that the apps can't know or care whether the device is rooted.