Blame it on global warming, seriously.
On a more serious note, i know exactly what you mean. However, it all comes down to demand.
Javascript offers a variety of features to add to the user-end of your website (
navigation, overall user interface, etc.)
Now all have browsing features, etc. in which
JavaScript can bring to
your website. After websites such as these offer such methods and such a technical-interface, it increases the demand. These are universal sites which offer
universal interfaces. For this reason, a lot of websites are trying to
grow off of their ideas/implementations.