It is absurd that there is no standardized UI toolkit, or rather that the web browser _is_ the standard with is characteristic _lack_ of user interaction idioms.
The fact that there are multiple platforms for UIs* is a huge failure of the industry as a whole. Apple, Microsoft and Google could have had a sit down together at any point in the last 20+ years to push some kind of standard, but they decided not to in order to protect their gardens.
*: a standardized UI platform doesn't necessarily mean a standardized platform. Just standardization of UI-related APIs and drawing.
My guess 10 or so years ago was that Google would be the first to bake Material UI into browser with web components, and then any browser would essentially reuse that to extend out whatever style they wanted. It really seemed like the way the web (and Google was heading). Instead we got bad Material UI knock-offs in about 45 different UI frameworks.