RHEL6 used upstart also. I had to write/maintain upstart files, too. systemd picked up steam inside Red Hat because of the number of edge cases upstart DID NOT handle.

It didn't do socket based activation at all. It didn't handle day 2 operations well (if you changed the configuration of some parent service and the children needed to be restarted, this was just as manual as sysvinit but with a clunkier format). overrides were terrible. Failing out on a depchain was problematic.

The debian politics never would have gotten there if Lennart (and others) didn't decide that it was easier/better to start from a clean slate instead of upstart's weird middleground of a "script" verb to kinda sort make transitioning from sysvinit scripts easier, but not a wholesale reconception of what an init system needed to be in 2015 or whatever year that was.

systemd was, in a sense, crowned because Redhat also tried upstart and had to suck lemons for an entire release/support cycle, wrote something better, and Debian followed on. Not because Redhat/others didn't try to make it work, or because of 7 people.