But also a consequence of having to float on top of non-free/uncontrollable base libraries. The only reason Nix works so well on Linux is because it can be in control of everything down to the kernel. For (presumably) this reason, nixpkgs will tend to only work well for one macos release at a time. There were also no pre-built binary packages for macos last I checked, so, having to build everything, if one dependency has a slightly flaky build procedure, it spells trouble.