Gradle seems to be an interesting case of a successful build system with an interface in a real language (Groovy), although Groovy is so dynamic that the line between Groovy and DSL is pretty blurry.
I think another big issue is the generally terrible interop between programming languages, each language has a silo of excellent libraries and the only way to move things between silos is with unsophisticated data formats.
I’ve also made a handful of developer libraries and always pick a cludgy data format for configuration, the ergonomics are quite nice—it’s easy to reason about as a user (no head scratching about what the config will look like at “runtime”), there’s generally no tooling setup required and no additional compilers or interpreters to install, and I’m free to use whatever languages as a tool designer I like and can move freely between them (at this point they all support YAML, JSON, et al). We want to make the barrier to entry as low as possible and simple data formats do just that.
