If you're an enterprise, do you see Canonical/Ubuntu or Red Hat as the most-credible vendor to support Systemd, which both of them are running? Is there anyone else who might hold that title? The answer to those questions are the point of what Red Hat's done (or else they've accidentally achieved a pretty amazing coup through a series of maneuvers that led to that outcome simply by chance, which notion strikes me as unlikely).
What's important is making it extremely expensive to launch or re-position a competitor distro to Red Hat that actually ships substantially-different software than Red Hat does, at a level of polish & reliability that might let you compete with them. It leaves competing distros as Red Hat followers. Which, fine if some hobbyists pick that, what they care about is being perceived as the only credible claimant to the title of first-party vendor of Linux, in most contexts by enterprise.
I'm surprised they haven't thrown in the towel yet at this point.
When I read HN, I never see anything positive about snap. And while this is arguably a fringe community, it is very highly correlated with the 1% of influencers to corporate decision makers.
Canonical-steered alternatives to Systemd, Gnome, and Wayland, have been advanced (as you note: Mir, Unity, Upstart) with less political and/or technical savvy than Red Hat's efforts, and have all failed. Technically they all still exist, in some form, but they're de facto dead. Snap/FlatPack is another place they're butting heads, and I think it's fair to say Snap's not got a bright future, but I guess it's technically still in the running, so we'll have to call that one undecided.