1. systemd (at least the PID 1 part) does not talk to the network, so a remotely-accessible backdoor would need to be more complex (and thus more likely to be detected) than a backdoor that can be loaded into a listening daemon like openssh.
2. You can run Debian systems without systemd as PID 1, but you're still stuck with libsystemd because so many daemons now link with it.
2. You can run Debian systems without systemd as PID 1, but you're still stuck with libsystemd because so many daemons now link with it.