Also, since when was Google "the" company pushing web UIs forward? Mozilla is that company in my mind -- remember the time when they made a whole mobile operating system based on it, and at the same time tried to push forwards for various parts along (WebBluetooth, other APIs)? That's what investing in the web as a platform looks like. Flutter is successful, but not in a way that plays nicely with anything else -- if you want to push a platform forward or encourage growth, doing things that play nicely with others even if they're less convenient for you is the way to go.
I'd love to be enlightened to what you think is the problem with DOM in particular that makes it not the right model -- TVML and UWP dropped the DOM, but basically replaced them with their own walled-garden re-implementations of basically the same concept. A quick look at the documentation for both and pages like collectionList[0] in TVML and the Getting Started page for UWP[1] look just like shitty HTML.
Ultimately, I can see why they would invent their own UI languages, because it means they don't have an external standard to comply with and can move pretty quickly. I think this is the major reason, not that those other markup languages they created are magically better than HTML's standard. Again, I think this is less of an indictment of HTML than it is companies trying to move as fast as they can without care for interop -- great for them, but probably bad for developers who have to learn all their little languages that are re-creations of an established standard.
[0]: https://developer.apple.com/documentation/tvml/layout_elemen...
[1]: https://docs.microsoft.com/en-us/windows/uwp/get-started/con...
Since they introduced JIT compilers for JavaScript, keep spending money pushing forward an operating system that is basically a browser juggler and introduced PNaCL.
> I'd love to be enlightened to what you think is the problem with DOM in particular that makes it not the right model
Rendering performance.
The way DOM semantic works is no match for a composition engine designed from the bottom up for accelerated graphics UI.
DOM is for displaying documents not interactive graphics.
This is also the main reason why Flutter team dropped DOM, at they were hitting the border of what was possible while keeping DOM semantics.
Also why Houdini project exists, but it is far from ever reaching the browsers.
If I am not mistaken it was Timothy Jordan that explained it on an interview.
So Google, the company pushing Web UIs, including PWAs in collaboration with Microsoft, still thinks they aren't worthwhile to be the default stack on their devices.
Apple and Microsoft also have UI stacks where JavaScript has first class support (TVML and UWP) and like Flutter, completely dropped the DOM.