JSON's rise in popularity was due to its utility as a data transfer format in heavy client web applications. XML is very verbose in comparison with JSON. Back when JavaScript interpreters were slower, this bloat was a big deal. XML just takes longer to parse, and in an environment where type coercion is the norm, a lot of type information, in the form of XSD, just doesn't make sense. When you own both ends of a communication pipeline, a strict contract, isn't really necessary.