Earlier quoted context omitted.
The only reason we have 10,000 UI libraries in the last 20 years is because we decided to keep default browser UI ugly and bare-bones for some reason.
That's a good thing in my opinion. Don't give me a set of 25 controls, instead make it easy to make my own. Because no matter what you include in default controls, I am going to need 12 more.
Like datatables, rich-text editing, toolbars,...
MOST applications are just simpler CRUD UIs. Developing these is still too complex on the web platform.