I think it became popular because you can deliver the same app to mobile and desktop platforms. And because js gave people a very easy intro to development on the web so tons of people know it.

I don't think it became popular because it was better at making an application on a single target. I've never made a webapp with the equivalent of GLADE or QtCreator so I don't know if it even exists - but those tools are very decent if you had a basic understanding of UI layout.