Systemd-networkd (not systemd the init system) defaulted to the google DNS servers when:
- the admin did not change the configuration
- the user did not configure anything
- the network did not announce anything
- the packagers had not changed it as they were asked to do
- the distribution actually decided to switch to networkd. Few have done somtomthis day.
That is indeed a serious issue worth bringing up decades later.
Yeah, sure... integrating a init system is a huge task (if you want to do it properly). Let's do that several times!