RDF is a directed graph model. Nowhere does it say properties have to have properties in a graph model. You can always model them as intermediary nodes.
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.