Arch Linux doesn't fork upstream projects and usually only does minimal changes/patches to a package. This means package maintainers spend the vast majority of their time packaging.

When you think about it, a Linux distribution should upstream useful changes to the original project and have the changes be available through configuration. But if that is the case then the vast majority of the code lives outside the Linux distribution. The package manager including the server backend might be the largest code base of Arch Linux and perhaps even the only one that has a meaningful size to begin with.