>Linux

More like Gnome and RedHat. In the BSD-y world and people akin on GNU (Alpine, Hyperbola, Parabola...) people loves the CLI and some stuff like TCL/TK or even Perl/Tk / Perl/GTK2. And the tools work well and fast enough.

Glade had a lot of problems, and core Gnomes devs really recommended against it[1]. I think that dev for Cambalache didn't want to try to figure that out.

1. https://blogs.gnome.org/christopherdavis/2020/11/19/glade-no...

If I had to guess I would say: more fun to develop a new system without any legacy code maintenance (GTK4 is a significant change in API). The idea with the new tool is to decouple the toolkit too so it will be fundamentally more resilient to churn.