Across a number of minority language communities I participate in, there's a constant stream of "Why isn't there a good native GUI toolkit in $MY_FAVORITE_LANGUAGE yet? All the ones I can find suck." questions, to which the answer is, you're asking for a project that can easily be on the order of magnitude of all the other Open Source projects in the language combined, if not greater. What you get with less than effort than that are the aforementioned "suck"y GUI toolkits. Which I celebrate and praise, but realistically, just getting a production-grade "rich text widget" is alone a staggering undertaking, let alone everything else that goes into a GUI toolkit.
Just a project to bind an existing GUI toolkit into your favorite language can easily overwhelm a dedicated team of multiple people, and as annoyingly complicated as that can be, it's wildly easier than building the entire toolkit.
Getting to "maturity" is a really, really hard problem.