This phenomenon is mostly because, as the article notes, Google has one of the largest C++ deployments in the world. And since much of the C++ code needs to be extremely platform-agnostic (any given library might be running in a web service, a piece of Chromium or Android, and an embedded smart home device), they tend to be very conservative about new features because their code always has to compile to the lowest-common-denominator (and, more importantly, they're very, very sensitive to performance regressions; the devil you know is always preferred to risking that the devil you don't know is slower, even if it could be faster).

Google can embrace modern processes, but the language itself had better be compilable on whatever ancient version of gcc works on the one mission-critical architecture they can't upgrade yet...