So why nobody is writing these "more complex" widgets? Really, react is here for a while and yet there is still no "solid" UI library.

Nothing with keyboard-friendly lists, data-grids and trees. And what about "controls"? How come I can't disable the whole form, including tabs and other controls, with just one attribute? Or a panel which can be detached into floating window?

Thats what I would call complex (and useful) widget.

BTW: This is what customers want (checktree, columncombo, dateragepicker, moneyfield with calculator, ...) https://www.tmssoftware.com/site/products.asp?t=vcl