We are discussing immutable distros, where you don't have apt/dnf/guix/whatever installed on the host system. They are replaced with other package managers. On Ubuntu Core, that is snap. On Fedora Atomic, that is rpm-ostree, flatpak, and toolbox.
MacOS is immutable, there is no non-immutable version.
MacOS's has been immutable for a while now. But that's not what I was referring to. Homebrew also works on Linux, lots of CLI tools and libraries are available there. It does have some GUI apps, but not as many packaged as for MacOS.
That's not the reason. On immutable distros, you can still mess up your flatpak packages, distrobox containers, homebrew packages, etc.
Only "OS" files like those in /bin prevent accidental modification and removal since you cannot directly change them, even with root.
It's not how you "generally" do it because many immutable distro developers keep developing additional ways to do package management that are more and more complicated.
I still don't get why we can't have a BSD like approach. Make usr, bin, sbin read-only. But have /usr/local be writable and have a traditional package manager install to that location instead.
Any program that takes in input has a greater chance of bugs that may result in security vulnerabilities. And I should hope that a text editor can take inputs...
So if i were to "sudo dnf install neovim" on Bluefin, that would install Neovim to ~/.local/bin?
I didn't mean to say that Universal Blue specifically was making new package managers, but that in general new package managers have been created specifically to solve problems introduced by going immutable/atomic/image-based/whatever.