These are set for testing/development purposes. For which the priorities are availability/reliability/speed. For those criteria, Google/Cloudflare are empirically the best worldwide.
This literally is used for test-resolving that at best probably would identify a systemd-dev. Everyone else shouldn't care because it's overwritten by distro maintainers.
I assume some of these use it.
>why the tests can't be modified to set DNS/NTP?
I am not a systemd maintainer, they probably could be adjusted, but frankly I don't imagine they or I care enough to do so.
Like I said, this change only affects the devs, so why should it matter to anyone else.
It's working anyway, i think it's resolving off the root nameservers...
I guess... You couldn't go more private than that.