> Why are so few configuration languages not backed by a real language?
There are tons of tools that work with YAML/JSON but I imagine you mean more like a first-class citizen programming language specific or good at writing static configuration. The other side of the coin is that configuration in many cases have a different audience than programmers (for ex, end users or operations team) and it's a good option to have static configuration key=value than any human can (more or less) read easily without having to run programming code in your head. Plus programming, besides being harder to read and share, introduces bugs. So I suppose the preference between code writing configuration and stand-alone configuration depends on who the consumer is and how complex the configuration is.
There are currently several options, like https://github.com/stripe/skycfg
> Why are so few configuration languages not backed by a real language?
There are tons of tools that work with YAML/JSON but I imagine you mean more like a first-class citizen programming language specific or good at writing static configuration. The other side of the coin is that configuration in many cases have a different audience than programmers (for ex, end users or operations team) and it's a good option to have static configuration key=value than any human can (more or less) read easily without having to run programming code in your head. Plus programming, besides being harder to read and share, introduces bugs. So I suppose the preference between code writing configuration and stand-alone configuration depends on who the consumer is and how complex the configuration is.