I think you are not familiar with how governments work. They are not going to rely on a random git repo, they are going to have contractors to ensure a basic level of support and bug fixing. And some contractors to ensure development and availability of tooling. And deployment and integration. They are also going to test, audit and validate updates, not just pull from remote.

Also, in some cases there are research agencies doing some work as well (sometimes they have been doing it for a long time on not-so-sexy but vital projects like Inria and the open source tax code in France).