As merely two examples, both gRPC and Kubernetes are important to Google, and yet Google opened sourced them. "No longer used" is not the criteria Google uses to make their software OSS.
FYI, I work at Google.
FYI, I work at Google.
Open source at Google generally takes the form of libraries rather than products. Often, that's something that an individual engineer is working on, and it's easier to open source than get the copyright reassigned (since Google by default owns any code you write). There are also libraries that are open sourced for business reasons - e.g. SDKs. You can tell the difference, because most individually-driven libraries contain the copy "Not an official Google product" in the README.
I found one after some searching: Nomulus. https://opensource.googleblog.com/2016/10/introducing-nomulu...
Go look at the manuals for IBM's Parallel Sysplex for mainframes and compare the simplicity of that to K8S for instance.
Or for that matter look at DCOM and the family of systems which Microsoft built around it which are truly atrocious but look like a model of simplicity compared to gRPC. (At least Don Box wrote a really great book about COM that showed people in the Microsoftsphere how to write good documentation.)
Or for that matter try doing something with AWS, Azure or some off-brand cloud and Google Cloud from zero (no account) and time yourself with a stopwatch. Well, it will be a stopwatch for AWS but you will probably need a calendar for Google Cloud.