Writing testing infrastructure so that you can just double workers and get a corresponding doubling in productivity is non-trivial. Certainly I've never seen anything like Google's testing infrastructure anywhere else I've worked.
Yeah Google's infrastructure is unique because Blaze is tightly integrated with the remote execution workers and can shard testing work across many machines automatically. Most places can't do that so once you have enough hardware that queue depth isn't too big you can't make anything go faster by adding hardware, you can only try to scale vertically or optimize. But if you're using hosted CI SaaS it's often not always easy to get bigger machines, or the bigger machines are superlinear in cost.
