Indeed, if you have a monolithic codebase releasing your code for other people use is much harder. In git it is possible to create a separate repository for it

Indeed, if you have a monolithic codebase releasing your code for other people use is much harder. In git it is possible to create a separate repository for it (using subtree and filter-branch). But the harder part is versioning and release management. At Google they avoid the cost of versioning their services and the release management around that, but this makes it really hard to have the outside world use their code. Maybe this is hard anyway since their code probably depends on a lot of services common to Google (GFS, BigTable). This is probably why they can't release Borg/Omega but have to make Kubernetes instead.