The irony is that systemd doesn't really follow what it prescribes in file-hierarchy(7), and expects some files in the "wrong" place. Other software has (obviously) followed suit, so now we're in a world where software follows the conventions that systemd _implements_ to maintain compatibility, rather than what it _documents_.

The most obvious example that comes to mind is /usr/lib/os-release, which file-hierarchy(7) indicates should actually be in /usr/share/os-release.