Cross-platform and being a good tool are orthogonal concepts. We use HTML/CSS for GUIs IN SPITE OF their general unsuitableness because the value of easy distribution wins over developer sanity.
> Cross-platform and being a good tool are orthogonal concepts.
I agree, but when I need to develop some software for Windows and Linux, a great toolkit for Android or iOS is of no use to me. Similarly, I won't use a Linux-only or Windows-only toolkit, as awesome as it may be, because I'm not going to build two different GUI layers.
Not cross-platform.
> iOS
Not cross-platform.
> Tk
Decreasing mind-share for 2 decades+, not something I'd start a new project with.