Package maintainers prefer appimages/snaps/flatpaks over native because it's as close to write once, deploy everywhere as we're going to get. Maintaining packages for distros is a thankless job often done by volunteers because there's no possible way for the developer to maintain packages for every distro.

The idea itself is reasonable enough: get some security by isolating packages from each other, and avoid python-style package conflicts by isolating dependencies as well.

Macs have been doing it for forever, and hardly anyone noticed.

Which leads to the real problem, that Canonical's implementations are consistently terrible.