I suppose it's because, whilst there are a wide variety of backend languages, JavaScript is the primary frontend language, at least for the web platform.
Edit: Or perhaps it's because JavaScript is finally becoming more popular, despite being old. Lots of new libraries and applications are being written in it.
A co-worker of mine postulates that most of this is client side Javascript, I'd be awfully curious to see how much of it is client side and how much is node.js and the like.
Edit: Or perhaps it's because JavaScript is finally becoming more popular, despite being old. Lots of new libraries and applications are being written in it.