The JVM problem was that it had applets and did not have the DOM integration of Javascript. I do often wonder if instead of Javascript in 1995 we had got WebAssembly and WebSockets.
Was it simply/easy? No. But, you probably wouldn't want to.. The DOM is a crappy way to build an application UI. Someday we might figure that out.
http://fxexperience.com/wp-content/uploads/2011/08/Introduci...
https://en.wikipedia.org/wiki/Extensible_Application_Markup_...
The HTML DOM sucks, but what other DOM is widely available and already installed on literally every machine on the planet?