Nothing should rely on how store paths are named, ever. Like, there is actually no reason to know that hash 1234abc is a certain output of derivation xyz-12.1.0. The contents of the store can be garbage-collected at any point. So you actively do not want things outside the Nix store (or managed by NixOS tools, or Nix-aware tools) referencing paths in /nix/store.
If you do something like write a config file that references /nix/store/1234abc-xyz-12.1.0/bin/xyz, that config file will break the next time you update the derivation that produces that path. Again, this makes knowing what things are in the store completely pointless unless you are writing Nix-aware tooling or debugging, in which case there are tools to show you what path your derivation produced. But you should never need to do the opposite, which is to resolve which derivation produced a path in /nix/store/.
The Windows Store problem is completely orthogonal; paths in /nix/store are not "installed" on your system, they are derivations or outputs of Nix derivations. NixOS "installs" things by adding some of these to your PATH in a shell script that is also a derivation output in /nix/store.
I'm afraid this doesn't work in a generic Unix world -- what stops an application from saving some env variable it was first initialized with into its local config and later accessing them (and potentially failing if they were GCd in the meanwhile)? E.g. many developer tools store references to compilers and the like.
Nix is over 20 years old. We've fought all those tools and won by now. (I.e. we've figured out how to configure them to not do that when we don't want them too.)
I am using Nix everywhere and have some packages contributed, so I do know how it goes - and there absolutely are cases like I have mentioned. Sure, apps can be patched, problems can be circumvented, but a fundamentally malicious/ignorant program can end up a pain in the ass for nix to manage (without bringing out the big guns like build FHS env)
Very well said, thank you!
I'm glad other people also understand that the onus of motivation is on granting some privilege, not rescinding it :)