Some trends and stats on sites that collect info on DE usage indicate that:
https://www.gamingonlinux.com/index.php?module=statistics&vi...
It's totally expected for me, KDE is just better if you want any kind of customization.
It also comes preinstalled on Steam Deck for instance.
From some of the big GTK applications I use are Firefox and Gimp. That's about it, most of everything else is using Qt or is in the process of switching to Qt in my experience (like Audacity).
And from the above, Firefox isn't really using GTK due to some integration with Gnome, they just didn't want to write their own Wayland handling bits. It works on KDE all the same.
