I think it’s worth asking ourselves why GitHub didn’t integrate Graphviz; maybe we can learn about our competitiveness. My guesses:
My guesses: Graphviz is in C, Mermaid is in JS, Mermaid is easier to integrate. Mermaid also has a few higher-level features (Gantt charts, Entity Relationship Diagrams, Sequence Diagrams).
While it’s possible to compile Graphviz to wasm/web-worker and embed on a website, it’s a pretty big library. There’s a bit of an impedance mismatch.
Finally I wouldn’t be surprised if the default styling played a part. Graphviz’s default styling is, well, spartan, while Mermaid’s is a bit nicer.