I think language embedding is kind of a lost architecture in modern stacks. It used to be if you had a sufficiently complex application you'd code the guts in C/C++/Java/Whatever and then if you needed to script it, you'd embed something like a LISP/Lua/whatever on top.
But today, you have plenty of off-the-shelf JSON/TOML/YAML parsers you can just import into your app and a function called readConfig in place of where an embedded interpreter might be more appropriate.
It's just easier for developers to add complexity to a config format rather than provide a full language embedding and provide bindings into the application. So people have forgotten how to do it (or even that they can do it - I don't think it occurs to people anymore)
But today, you have plenty of off-the-shelf JSON/TOML/YAML parsers you can just import into your app and a function called readConfig in place of where an embedded interpreter might be more appropriate.
It's just easier for developers to add complexity to a config format rather than provide a full language embedding and provide bindings into the application. So people have forgotten how to do it (or even that they can do it - I don't think it occurs to people anymore)