In reply to Rick.

On the other hand, we can sit here, write essays about who should be writing documentation, and not get anything done at all. How about we take the route of getting more volunteers involved with core?

Nevertheless, the Customizer API has been documented. It's just now better documented, which is awesome! I still encourage more people to get involved with writing tutorials and documentation. Writing about a subject is actually a great way to learn more about it.

Also, TRT (not TMT) didn't author this documentation. Although, some people involved with the team have written tutorials on the subject in the past.