Well why have two completely different ecosystems for the wbe and desktop/mobile applications, especially in terms of UI? Both can network
We have seen all these framework claimed to be cross platforms and none of them are not able to make it to the top framework being used.
Web is the only "platforms" with some kind of success by abstract everything away so most of the browser display roughly the same things to all users on all OS.
Implement the UI framework at an OS level. The default OS-specific design should live on top of that. If you were to build an OS of the future, there shouldn't be this need for this distinction between web and desktop.