There are libraries at least for Java (which should be usable from Kotlin, right?), Ruby, JavaScript, Go and Rust.
I agree the lack of libraries is a pain, but Markdown, except for the basic functionality, is also devoid of compatible libraries (i.e., each library implements its own superset of Markdown that no other does).
If anyone wants to write an Asciidoc library with just the most basic features that should be easier than writing a Markdown library.
I also think Asciidoc has way too many features and maybe we should restrict it to a subset, ignoring complicated stuff that no one ever needs.