systemd is linux-only

There's no real debate as you have to go upstream against the distro to support sysvinit, no? The heart if the matter when it came to the Debian vote is that systemd only works on Linux, where other init systems including systemvinit are cross platform. The systemvinit originally came from System V Unix, such as Solaris or Unixware, so it definitely is cross platform.

Given Debian distros run on more than just the Linux kernel, it was an issue to adopt a Linux-only init system at the time. But in the end, systemd won out by a narrow margin, and this impacted downstream distros like Ununtu and Mint.