At Google, tens of thousands of software engineers contribute to a multi-billion-line mono-repository . This repository, stored in a system called Piper, contains the source code of shared libraries, production services, experimental programs, diagnostic and debugging tools: basically anything that's code-related.
This open approach can be very powerful. For example, if an engineer is unsure how to use a library, they can find examples just by searching. It also allows kind-hearted individuals to perform important updates across the whole repository, be that migrating to newer APIs, or following language developments such as Python 3, or Go generics.
Code, however, doesn't come for free: it's expensive to produce, but also costs real engineering time to maintain. Such maintenance cannot easily be skipped, at least if one wants to avoid larger costs later on.