Even in the old desktop world someone had to build the button widget (and all the others) that let you just throw stuff together in MFC or Swing or whatever.
Same today - someone has to build the web components in order for us to declaratively use them as high-level Lego.
Trouble is, there is no real high-level "general purpose" library of components beyond the core HTML elements (they'll get you a long way but there are notable things missing that we expect from apps, e.g. toolbars, menus, tab strips etc), and then the probably reason for their not being a general high-level library is that everyone wants something special for their websites (because historically websites have always allowed a lot of design flexibility, way more than your typical win32 app ever did for example).
I have several times really wished to have some solid "desktop style" components to use for things like menus, tool bars etc. That would make prototypes in electron/neutralino/tauri way way way faster to do.