Of course, the actual hacker was to blame, but systemd was implicated. The fact that the attacker was willing to settle for compromising just Debian and Red Hat

Of course, the actual hacker was to blame, but systemd was implicated. The fact that the attacker was willing to settle for compromising just Debian and Red Hat systems indicated that they perceived the path from xz to libsystemd was the easiest way to effect the backdoor and that doing it any other way would have been too much work for marginally little gain (Red Hat and Debian systems being so common).