> HTML is almost frozen in carbonite.
Not really - there are pretty big escape hatches - you can do pretty much anything in canvas, custom elements allows you to define your own elements with their own behaviour.
I'd say the problem is the opposite - one of the reasons desktop apps from 20-30 years ago ( say MacOS 7 ) where great from a user perspective is pretty much all apps looked and worked in the same way, using the same UI toolkit and the same UI principals. And from a developer perspective - a lot of the key decisions had already been made for you.
The web of today is a zoo of UI styles and interaction modes.
The problem isn't so much a lack of innovation or possibilities, but perhaps rather the opposite.