It is more an expression of confusion rather than type system quality evaluation, but why does JSON parser's implementation returns its own types like JsonNode?

It is more an expression of confusion rather than type system quality evaluation, but why does JSON parser's implementation returns its own types like JsonNode? Why doesn't it just return core types like: * JSON String -> NIM String * JSON Object -> NIM Hash * and so on... I've also had the same question when looking at https://crystal-lang.org https://crystal-lang.org. PS: I do not claim Nim's type system to be bad as I do not have an exact counterexample of a "better" type system.