By far my number one reason for hating Ubuntu is that a lot of lazy software publishers think that only supporting Ubuntu is good enough to reach Linux users, even though (as this article points out) they're one of the more contrarian and overall difficult to work with distros in the ecosystem.

Its less of a problem today thanks to containers. Even when a dev doesn't publish a flatpak, you can usually run it in a podman/docker container, or in a toolbox/distrobox.

Still, it pisses me off when I see that happening (even though it's technically not Canonical's fault)