Why widget-centric web frameworks aren't that popular?

I'm talking about frameworks like Vaadin (Java), Wt (C++), Reahl (Python) and etc. In my opinion these frameworks are much easier to code in (you code in one single language without the need to know JavaScript, HTML and CSS) and to understand (the usual GUI development approach based on widgets is much simpler for a noob to understand than MVC or MVVM). Why aren't these frameworks as popular as mainstream ones? Btw is there any of this kind of frameworks that I missed? For example I haven't seen one for Ruby, Go or other commonly used web development languages.