Because the portals repository is a submodule in mediawiki-config, the submodule is pegged to whatever commit is specified by the parent repository ( and updated by commits like this). This means that https://www.wikipedia.beta.wmflabs.org/ only reflects the change that happens right before a deployment, when mediawiki-config is updated.
It would be more useful if https://www.wikipedia.beta.wmflabs.org/ was a reflection of the head of the portals master branch.
This can be achieved by running git submodule update --remote portals in the wikimedia-config repo.