Yep. In fact, less developers are using GTK (and migrating their projects to Qt[0]), and less users are using GNOME, over time due to its self-imposed limitations. KDE usage, in what metrics I've seen, is somewhere at parity with GNOME for DE market share and growing while GNOME is declining, which is telling given that KDE is not the default DE in major distros.

Synthetic "popularity by default" vs. authentic popularity at work.

0: https://en.wikipedia.org/wiki/GTK#Criticism