1. People don't want to learn bespoke languages.
2. You have to build all the ecosystem tools for a language (compiler, docs, language-server, IDE integrations, dependency management)
Similar endeavors are WaspLang and DarkLang, which I have yet to see in the wild or (meaningfully) on HN. Better to use an existing language and focus on the value add.
I personally built something with similar value add (source of truth -> all the things). I've been through some of these pain points myself.
https://github.com/hofstadter-io/hof
The idea is CUE + text/template = <all the things> (not limited to APIs)