(i) These structures are supported, all modern programming languages.
(ii) The JSON standard is language-independent and its data structures, arrays and objects, are universally recognized.
(iii) These qualities make it an ideal format for data interchange on the web.
(iv) JSON is easily readable than xml.
(v) JSON is fast than xml.
So, now Web Services and API.s use JSON format to provide public data like facebook, twitter etc.