Many of those assumptions are standards such as the filesystem hierarchy (granted, that's an xkcd 927 situation), nix is a bit of a special snowflake that breaks things in subtle ways (e.g. [0][1]) and needs workarounds in various places. Those workarounds are not necessarily onerous, but they would be unnecessary if it didn't deviate.

[0] https://github.com/NixOS/nixpkgs/issues/420513 [1] https://github.com/NixOS/nixpkgs/issues/94228