The graph database is still in its infancy and there are a lot of graph query languages about. We played around with using some that already exist (especially SPARQL) but decided that we wanted a number of features that were very non-standard (such as CLP(fd)).
Using JSON-LD as the definition, storage and interchange format for the query language has advantages. Since we can marshall JSON-LD into and out of the graph, it is easy to store queries in the graph. It is also very simple to write query libraries for a range of languages by just building up a JSON-LD object and sending it off.
We are firmly of the belief that datalog-style query languages which favour composibility will eventually win the query language wars - even if it is not our particular variety which does so. Composibility was not treated as centrally as it should have been in most of the graph languages.