https://www.hillelwayne.com/post/graph-types/ gives an interesting take on why we don't see a graph type as a primitive on more programming languages. Essentially boils down to graphs being very vague and depending on the topology of your graphs you are going to want different implementations for reasonable efficiency.
Interesting! Thanks for the link. I suppose the graph databases just take an opinionated approach. NetworkX is great; I always wished it had a simple backend.
That said, there are graph databases.