On the contrary, Nixpkgs is generally made by the most pragmatic people and takes a flexible approach to a lot of issues. For instance, very few package managers have packages for proprietary software like 1Password in their official repositories. Nixpkgs also doesn't insist on building everything from source when it's hard to do so. As a result, Nixpkgs contains many packages for NPM or Maven projects. Other package managers insist on packaging all its dependencies from source, which is why they're struggling to package software written in modern programming languages.
As for 1Password, it works fine on NixOS. When installing proprietary GUI apps like 1Password on macOS, I just use Casks. I suspect many people do the same, which might lead to the 1Password package not working as well on macOS because fewer people bother with it.