I assume because it’s not on the top priority list. After all the development and docu updates are done by volunteers. Seems like no one voluntered to update it so far. Everyone can actualy “edit the page”, which forkes the docu project on github. Once finished with the changes, a PR will put the changes on the radar of whoever is permitted to handle PR’s.
From what I remember correct schema version 3.9 extends the schema with a windows container related new feature.