Contrary to what people seem to think, just because GTK+ compiles on Windows and OSX, doesn't mean we are trying to be a cross-platform toolkit. Many GTK+ developers consider GTK+ to be a platform in it's own right, not a portability layer.
But you might want to discuss updating https://www.gtk.org/ and other sites for that matter. Quoting the first lines of the home page: "GTK+, or the GIMP Toolkit, is a multi-platform toolkit for creating graphical user interfaces".
I disagree with the current GTK direction, but it's not my project and I accept that. If the focus of the project has changed, update the website(s) and documentation.
Also the HTTPS stuff pointed out by distances.
The content only seems to be served via http.