"Burden" is an understatement. Any API Microsoft documents becomes part of their ongoing commitment to eternal backward-compatibility. (Heck, even some things they never document at all still end up forced into that commitment, like the internal registry hives in Windows 95.)
So Microsoft do everything they can to only document what they're absolutely sure they have in a good, stable, "won't regret later that we didn't fix it some more before setting it in stone" state.
My guess is that it's due to one of the following:
* The API isn't considered beta yet. * This was created as somewhat of a side project and hasn't been formalized yet. * Documenting it is on the backlog. * It's meant for internal use in that they may be building in tools in the Security and Compliance center that will be calling it.