If Gnome cared about an easy to maintain codebase it would be radically different. Gnome's complexity is comparable to a large web browser (which is kind of insane considering how little it really does.)
Obviously it's a bit hacky and kind of a mess, but it is technically interesting.
When I say GTK has bindings for every language, I do literally mean every language. It's the nice thing about choosing C as the language to make your entire API in.