Think Autodesk products. Certain parts (wasm modules) only load when you hover over a menu while overall app loads within milliseconds because it just has the main window and such.
HTML is declarative. The machine understands it. I like things machines can understand and optimize. Things that you can write automated tools to work with because it's not a full turing machine. If you want to make a screen reader, you can. If you want to reflow for mobile in a better way, you can, because you know what's text and what's an image.
Just giving people a programming environment and the ability to draw some pixels, the browser has no idea what the intent is. There's nothing to optimize unless the individual sites do, and I doubt they have Google and Mozilla's budget.
We already have too many unnecessary powerful imperative systems out there.