Comment by smilingleo

I think context matters, often I might be writing docs in a text format that doesn't support mermaid (some readmes for instance, or a print put in a CLI tool) and want diagrams.

In those contexts, rendered mermaid as html isn't an option, so this really does seem like one of the best calls for human readability.

You can put ASCII diagrams in code comments.

Also Claude code in the terminal can show them.

What you mean is that you don't find ASCII diagrams useful. Other people do (see other comments). I find them useful for Org Mode where I prefer to work with just text instead of having to keep separate image files together with my .org files. They're also easier to work with if you need to check them into a Git repo and you don't want to be bothered with something like Git LFS or git-annex. The fact that there are people who want them is enough to explain "why there's a push toward" them (assuming there is actually such a push).

A lot of people primarily use markdown and command-line, and, importantly, so do many coding agents (which seems to be the authors' primary use case).

They don't need a renderer, so they can be embedded in source code comments, or in markdown document without requiring e.g. Gitlab to properly render the document. And even then, they're still "rendered" when editing said markdown document.