A lot of it comes down to robustness. Neo4j has the advantage of simplicity and maturity when compared with multi-model dbs. Multi-models, as of now, are feature rich and reliability poor. Instead Neo4j has fewer features but just tries to do those things really really well.

It's been in mission critical prod. environments now for nearly a decade. I'm certain that in the future DSE, Orient, Arango, or someone like them will be big contenders in the space. However, for the time being, I wouldn't trust anything critical to them.