Most user interface elements can be described as a tree, so you inevitably will end up with something like XML. It is just an accident that HTML got popular. Because of the federated nature of web it impossible to upgrade all websites to use modern HTML5. Even now most 70% sites are still using HTML4. After many  browser wars … the browser market has consolidated around Webkit but this lead to a bloated JS API.

The failures of Html

• Poor layout algorithms
• CSS is a bad idea (see CSS-in-js, tailwind)
• Can’t customise DOM elements, because of which you can’t have a visual builder

In many ways Flash is what the web should have been.