Others have mentioned generation and speed, but there's a much more important piece, IMO:

Maintainability. With declarative text-based diagramming, you can check these in as text files, and when the system evolves or the diagram has a need to change, it's easy to make a change and re-generate the image.

This. With the right tooling, you can embed diagrams as part of a larger document using a code block, which can be tuned and maintained as the system it's describing changes.

Once you learn the rules for the type of diagram you're making, it's much simpler than opening up <diagram tool of choice> and trying to shuffle the pieces around to make room for the change, or re-sketching the whole diagram from scratch on a piece of paper.

You’re catching shit in part because the “strange language” is a kind of standard tool in its niche (automatic graph layouts & drawing). It’s called “DOT” and may be regarded as venerable, if a touch obscure.

See:

https://www.graphviz.org/documentation/

People who use Graphviz tend to know the basic Graphviz language, but, probably more importantly, it's easy for tools to generate it.

Absolutely this. If I'm making a diagram for a presentation I'm going to draw it manually so it looks just right. When we're debugging dataflow graphs with 4000 nodes, graphviz is the one and only.

Thanks! A lot of the good stuff (e.g. stress majorization and the Jaccard distance model stolen for neato -Gmodel=subset) was done in the 2000s. Probably people criticize because they see B&W graphics, Times-Roman and splines rendered 1pt wide and we didn't use XML or JSON.

Drawing a single diagram will be faster, true. But adding even a single new node which requires re-layouting the whole thing to make space would require you to redraw the whole diagram, whereas in Graphviz/DOT it’s literally just adding one line of code.

I literally started using GraphViz last Friday, and I'm never giving it up now. My handwriting looks like I've spent the last twenty-five years typing. GraphViz gives me maintainable and updatable diagrams. I just installed the MediaWiki extension on our internal tech wiki.

Not if you're trying to use it in a slide show, or share it with other people over email. I work in a high security environment, so even if I could draw it better/faster by hand, I cant pull out my phone and take a picture.

You might be wrong about this; you should try graphviz to find out.