I'm taking about the "Recommended for most users" tag for the GNOME ISO.
Looks like the main reason GNOME is recommended for installation media at the moment is that it does a better job of autodetecting HiDPI displays, and then scaling appropriately: https://github.com/NixOS/nixos-homepage/pull/643
There are also some packaging issues for Qt with NixOS, because Qt plugins fundamentally rely on ‘impurity’ at runtime, and the Qt framework makes promises it doesn't keep about binary compatibility.
Here are some of the relevant issues for historical context and some of the tradeoffs Nixpkgs developers have faced when it comes to handling Qt and KDE packaging:
https://github.com/NixOS/nixpkgs/issues/86369
https://github.com/NixOS/nixpkgs/pull/54525
https://github.com/NixOS/nixpkgs/pull/44047
I realize that may not be a fully satisfying answer as to why the GNOME-based installation graphical ISO is recommended over the Qt one because one can imagine that the Qt packaging issue should be resolved some other way, or see the difficulty of packaging Qt plugins and applications in Nixpkgs as fundamentally a Nix defect. But I hope it makes that decision make more sense.
FWIW, afaict Plasma is the more popular of the two major DEs on NixOS, and it's what I've always used on NixOS myself, including now. It is definitely usable.
It does but it's rather unfortunate that the only choice we have when it comes to DEs is either GNOME, which is built by a group of arrogant developers who think there is no downstream for GNOME and GTK, and KDE, which has technical issues that prevent widespread adoption.
Which KDE technical issues are preventing its adoption? I'm running KDE full for a long time and encountered no issues.
IMHO, the lack of KDE adoption is the inertia of GNOME adoption by the major distros combined with the inertia of hate over KDE with the stereotype that "it's bloated" which hasn't really been the case in the last versions of Plasma.
Some of them are linked by pxc post above mine.
There's also the issue that Qt apps can only be written in C++, a language that many don't want anything to do with. In comparison, GTK has bindings for a variety of languages including Rust.
Are those good bindings , or auto-generated or outdated ones ? I did not checked in a long time but I think only Python had decent bindings. I would avoid non-official bindings, those are most of the time garbage and you waste your time instead of focusing on your work.
I seen Qt in a lot of proprietary applications, including launchers for video games (the app that will let you setup a game configuration before launch) - I was surprised why a Windows only video game would not use the Windows APi directly, but it is obvious that Qt is better then whatever Windows has this days for c++ devs and game devs are not afraid of a bit of c++ or have some irrational disgust for Qt pre-procesor (I see this excuse all the time, we don't switch from GTK to Qt because of the qmake/moc I honestly prefer an honest explanation)