They have a healthy ecosystem of both open-source and commercial software, and unlike property graphs were designed with data interchange in mind from the outset.
SPARQL was the first and still is the only standard NoSQL query language.
While RDF forms a graph, it is not a general graph model. In particular, two things that are enabled by graph databases (having data in the node itself, and associating data with edge) are not directly possible and need tricks such as relationship reification.
On the social side, the sectarism and bikeshedding tendencies of the community can be another turn off.
Naming of nodes with IRI is also a ridiculous, especially in Linked Data where changing your hosting domain (and even the protocol to access data) requires changing the data itself.
Show me a definition of a "general graph model"? Nothing shows up on Wikipedia.
There is on the other hand a directed graph model: https://en.wikipedia.org/wiki/Directed_graph This is exactly what RDF is, with labeled vertices and edges.
The thing is you can’t represent "A"->"B" directly in RDF. You need to stretch the representation to at least use a resource node as subject, but also for the object too if this node could be used as subject in another predicate. And of course both these resources must be encoded as IRI and then linked to the literals that contains the data. That’s four nodes and three links instead of two and one. It’s a lot of boilerplate code for a simple problem. And as said before, putting key:value on an edge require reification of the edge... which undermine the simple SPO model because it’s now SP(O as P)PO.
You may think it the same but it’s not. Usability matters and that’s why the SemWeb stack has almost zero adoption since its inception while graph databases are trendy.
Where is my LOL GIF :D
RDF Knowledge Graphs used by: Elsevier, Bloomberg, Thomson Reuters/Refinitiv, Uber, Zalando, Microsoft, Apple, Amazon, HSBC... do I need to continue?
If you mean "mainstream developer" adoption, that is a poor and irrelevant indicator, because mainstream is not where the innovation happens.
OWL was a foolish mistake. Triple is a clean and simple idea, but in practice -- reification and URI character hell becoming mind numbing. The RDF-guys did nail it with SPARQL. That is such a pretty query language. Simple, intuitive. I haven't studied the recent path expression advances. I should.
But yea, lots of ways of fugglin' with the data.