Defaults matter a lot, and snaps are the default in Ubuntu.
The topic is not whether snaps are avoidable or not, but the Ubuntu is going downhill. And snaps are purported to be part of that downhill, which would be Ubuntu's NIH syndrome. As far as I know, Ubuntu's only successful development is Ubuntu itself - the other projects have all failed over the years, and snap, while ongoing, is not winning any popularity contests either.
> which would be Ubuntu's NIH syndrome
Red Hat do the same. They reinvented the wheel on multiple occasions (systemd and it's whole ecosystem like systemd-resolved and timed and the whole kitchen sink; podman, buildah, dnf, etc etc.)
They just have more success on getting their NIH babies accepted as the standard by everyone else. Canonical just fail at that (often for good reasons, Unity was downright crap for some time) and abandon stuff, which doesn't help their future causes.
Snaps per se are no better or worse than flatpak. Canonical's mistake, IMO, was to make their store the only place snaps can be hosted. That is the "proprietary" bit everyone keeps talking about.
But in practice even for flatpak the only realistic place you can publish your flatpak if you want any traction at all would be flathub, so both formats have only one store right now. But flatpak allows a custom store while for some strange reason Canonical decided not to allow snap that freedom.