The maintainer and contributors have full-time jobs. On the one hand, part of that job is keeping up Scalaz for their own professional usage. On the other hand, no part of that job is documenting it for everyone else.
Really now? As if these guys get paid to do create and fix scalaz all day right? Like Oracle yeah? This is the story about every single open source project. You can choose something else, wait it out for documentation, or contribute it. Lucky you even have the source!
It's possible to make them typed with the stdlib[1]. Link also gives some reasons as to why they're untyped. Short answer is it started as a way to replicate Erlang in Scala[2].
What's the point of having a powerful type system like Scala's and then throw it out of the window just so I can use a distributed framework?