I don't know exactly but none of the diagram building languages I've used have been a great experience. I guess they just feel "rough in the hands" somehow to me. There's always some point of frustration I get to with the layout systems. They're essential for quickly visualizing graph structures and such but even smaller hand authored ones end up feeling unwieldy too. Can't put it in to works but it feels like there could be a major improvement beyond what even D2 studio offers, when it comes to the language and workflow around it.

I feel similarly about charting libraries.