I know one of the GTK developers who dropped out of my research group in the 1990s who's been in charge of triaging tickets and he's the kind of guy who doesn't care if there is just 1.05:1 contrast between text and background and will refuse a one-line patch to make menus render right in rootless X windows because he wants to punish you for doing things in a way he thinks is wrong.

And he probably wonders why it is never "the year of the Linux desktop" but hey it is OK because Red Hat Linux is something enterprises subject their users to and if it had the slightest bit of flair customers would complain.

So when I hear GTK I think Nein Danke!

In general Linux has the kind of fanbois problem that MacOS had maybe 10 years ago. There are so many things that still "just don't work" after years and they never get fixed because you can live without them. For instance I can tell you how to install some package like

   sudo apt-get install mypackage

and that's all! I can make 10 pages of screenshots to tell you to click and click and click and click and click to install "mypackage" with the GUI [1] and you may wind up looking at a spinner for 10 minutes or longer (eventually you give up) and you might wind up corrupting your package database and not being able to install or update anything until you look up how to rebuild it. The Linux desktop is stuck with having done the 20% of the work that gets it 80% done and never does the rest of the work because you can use the command line anyway.

[1] and you still might misunderstand it and need intensive tech support