Desktops can be installed on any ubuntu release. you could install xfce on kubuntu, or kde on base ubuntu. And what DE/WM you are using doesn't matter in a quite a few scenarios, so it's not worth bringing up in the same way that I don't mention "Im using cachyOS niri wm"

I personally preferred xubuntu over kubuntu back in my *ubuntu days. etc etc. there are a lot of spins of ubuntu and when the only differentiator is DE (which you can also just install on base ubuntu), it's easier to just talk about them all as a single overaching entity/family ... ubuntu.

Talking about kubuntu inherently requires talking about KDE and ubuntu both, so people just skip the KDE discussion.

"Too many distro options" is already a complaint of a lot of non-linux users, so specifying every last spin can just drive people away.

Discussions that I've seen (not here necessarily but in general) seem to bring up Kubuntu as a light weight option for systems that can't handle the more "bloated" vanilla Ubuntu. And it's why I put it on an old MacBook I had, because other mainstream Linux flavors were a bit much - no, I didn't try Arch, I'm also still a beginner technically. Kubuntu works great without overloading it. Doesn't mean you can't use it on a more powerful system of course.

My only regret with using Ubuntu for my main is some issues I've run into with Snap, but I'm learning how to figure that out and find alternatives like Flakpak, Apt, or using an AppImage when it fails me or seems broken. The lack of updated versions has been the biggest problem. Other than that, the OS itself has been running great. I did have to go with 22.04 because 24.04 just refused to install correctly, had 22.04 also given me problems I probably would be with a different distro.