Not all. Nix and guix allow you to install packages into your own profile as an unprivileged user. Best of all, packages that are installed by multiple users are shared in the Nix store.

The sole case that leaves are cases in which your company doesn't allow you the necessary privileges to install software which is an organizational challenge not a technical one.

That said something like nix can allow you to install software per user.

The way I see it, a system is a stack: that is you put a number of layers on top of each other.

The kernel is a layer at the very bottom, on top of which you stack a distribution. This distribution is managed through a package manager. On top of this distribution you could stack a user package manager.

In this view, you cannot compare apt or yum to home brew, they don’t belong to the same layer.

If you think about it, that makes sense. User package managers have to rely on the underlying layer to provide tools for e.g. compiling user packages.

Now I agree that in real life, the limit between layers can be more blurry:

- system package managers distribute end users softwares. Because most desktops are single user so having an extra layer is often not necessary.

- some system package managers are re-purposed to be stacked as user package managers. E.g. you can use gentoo prefix.

Still, to have a clear picture in mind the layers should be considered.

That being said, there are a bunch of user package managers you can also use on Linux. Have a look at spack for instance. I think the nix package manager can be used like that also.