Now that we have a web-aware platform (which NeWS was not), nothing stops us to create good UI tools on top - yet it is happening very slowly.
Also there is big performance impact, where piling up divs with CCS requires the right incantations, some browser version specific, for hardware acceleration to kick in.
And in any case, it is impossible to fully replicate the UX of the host platform.
How well does that work when your GUI must be shown in arbitrary devices, with arbitrary screen sizes and arbitrary resolutions? And how well does it reflow when the user changes the viewport size?
In any case, the original post to which I replied was comparing HTML5 to the NeWS platform, which provided a unified UI stack itself, so you wouldn't be able to match the native behavior following that approach either.
You are missing the fact that NeWS offered this kind of control.
"The NeWS Book" - https://archive.org/details/bitsavers_sunNeWSThe_11666863
https://www.usenix.org/legacy/event/usenix2000/invitedtalks/...
https://en.wikipedia.org/wiki/NeWS
There was a simplicity and purity in its approach to front-end interactivity and rendering that completely eludes the HTML+CSS+JS stack we're now stuck with. As the Wikipedia article states...
"NeWS was architecturally similar to what is now called AJAX, except that NeWS coherently: used PostScript code instead of JavaScript for programming; used PostScript graphics instead of DHTML and CSS for rendering; used PostScript data instead of XML and JSON for data representation."
PostScript is basically a graphics-oriented Forth, so it's kind of a weird language to write directly... But it would have been great as a target for all sorts of interesting compilers and GUI tools.