Many software decisions are more about strategy than philosophy. Compromising on ideals and principles to gain adoption. As mentioned before, I would not be surprised if dependence on machine-id was simply strategy.
Systemd might be replaced in future. But currently it's used in all major distros. It's design and ideas will probably inspire whatever replaces it. If they had spent their time clinging to philosophy and ideals rather than making compromises, then they might have never left the ground.