Those vars require editing nextcloud’s config.php. The official image can afford to mess with them, because their docker dev team can work closely and coordinate with their app dev team on changes from version to version.
We can’t afford to mess with config.php because upstream changes can and will break our scripts that edit those.
Since all those settings are only done on first run, and most of those are done through the wizard, it’s not worth the risk for us to create vars for them.