Well, many of us did try various distros and in the end switched to Ubuntu because it was really the only one that "Just worked".
Now it's possible that's changed and Slackware or Fedora or Debian "just work" but I'm not getting that feel from what I'm reading of any of these distros. I'm still hearing the same moans about stuff that isn't quite integrated. The tragedy with Ubuntu is that it's slipped and is heading towards the lack of quality we saw with distros five years ago.
In any case, the point is that Ubuntu works the way we want. So our first choice is always going to be something that works the way Ubuntu did until it started to get annoying.
BTW my other problem with the OR (original reply) was that it assumed that we want to punish Canonical for daring fail us, and that's why we wanted to switch, to send some kind of message.
But I don't want to. Actually I hate the idea of treating Canonical in that way, I'm reluctant to switch to Mint, and if there was a GCUbuntu (like Kubuntu or Xubuntu, but with the new Gnome Classic system) I'd probably jump on that instead - leaving aside the ease issues of switching to such a branch.
Why? First, because Canonical did such a great job in the beginning anyway. For a time, we genuinely had a platform that was close to being as usable as the most usable platform (Mac OS X) while having the flexibility, power, and support of the most popular platform (Windows). And Canonical has been a victim here not of hubris but of a lack of it. It wanted to do better.
I like the fact it wanted to, and I like the fact they tried. I think Unity brings great ideas to the table, the problem is it doesn't, ultimately, work. It's not a good system. The Mir/Wayland fiasco is another example, not just of Ubuntu but of the community as a whole, that sees problems with X11 and wants to do better, but again I just don't see how it's better - impossible to measure in the real world benchmarks do not a better display platform make.
I think there's a call for GCUbuntu, and I hope it's heard. And if I do switch to Mint I'll be doing so reluctantly, hoping that Canonical can get things right over time.