At least from an outside perspective, Ubuntu is Canonical's thing
In some ways, Ubuntu and Debian look pretty similar to each other. They use more or less the same set of packages (because Ubuntu is mostly based on Debian packages) and they operate relatively similarly, to the extent that we could probably replace our use of Ubuntu with Debian without noticing much change. But there is a big difference. Debian is a community with a particular long-standing philosophy and set of practices, while Ubuntu is Canonical's thing, not a community.
It's true that Ubuntu has a community of people who contribute to it despite Canonical not paying them for their time and work. But this community doesn't get to make real decisions on anything that Canonical cares about, any more than the CentOS (community) board gets to overrule IBM's views on how CentOS should operate. If and when Canonical says 'Ubuntu is doing X' (or 'not doing X'), that's what happens. In a way, there's nothing particularly nefarious about this in the case of Ubuntu; Canonical founded it and has always paid for it and run it, and we've just enjoyed the ride.
(There are benefits to being on Canonical's ride. Contrast the extremely regular and easy to plan for Ubuntu LTS release schedule with the somewhat more anarchic and unpredictable Debian release schedule, for example.)
Or to put it simply, Ubuntu is a Canonical product that Canonical has managed to attract some outside contributions to (beyond PPAs).
As far as I'm concerned, this means that I'm much more inclined to blame Canonical for various aspects of Ubuntu (including the periodic package roulette) than put it on anyone else. Canonical "owns" Ubuntu in a way that no one else does, and so they get to be blamed for the effects of all of the decisions made on Ubuntu. Either Canonical made them, or Canonical didn't care enough to pay attention.
Would some aspects of Ubuntu be better with more community work and contributions (for instance, more actively moving package updates from Debian into Ubuntu LTS)? Assuming that Canonical allowed them, probably, but it's hard for me to see how Canonical could attract them, since if you work on Ubuntu you're voluntarily working on Canonical's product for free. I would expect many people who want to make significant contributions for free to go work on Debian instead.
Perhaps this is not quite how Ubuntu really works. If so, how Canonical (and the community) operate and talk about Ubuntu don't make that at all clear to outside people. It certainly seems that Canonical routinely speaks for Ubuntu, and major technical decisions are routinely made by Canonical (for example, netplan).
(None of this is exactly news, but I feel like writing it down.)