systemd's widespread adoption was somewhat controversial and took years. I realize Upstart didn't receive widespread adoption, and Canonical has historically liked to start its own products (Mir and Unity as you noted). But the discussion around systemd was not "everyone except Canonical thinks it's good", and Upstart had been in development for several years.

Wasn't it Canonical creates Upstart, switches Ubuntu to it, RH switches to it; a few years later, RH creates SystemD, RH switches to it, Ubuntu switches to it?

Do you want Canonical to just adopt whatever the new hot RH stuff as soon as it's stable?

You do want to know the alternative is stable and better for a few years before even thinking to make the change.

It's easy to laugh at the history after it took place.

But the init system was Upstart. Upstart, like SystemD, can start daemons from SysV scripts. At the time, the majority of distros still used SysV or SysV-like init systems. As long as the newer systems had backwards compatibility with the SysV scripts and the newer functionality were not needed, why would upstream switch to the new format?

SystemD has managed to gain near-ubiquitous usage, to the point where plenty of upstreams now only ship systemd unit files, but I would argue that this change was first initiated by the introduction and adoption of Upstart in both Ubuntu and RH.

We tried to use Upstart properly in Fedora. We spent three Fedora releases trying to do that (Fedora 9, Fedora 10, Fedora 11, and Fedora 12). We gave up by Fedora 13.