Its both. The tooling has a very direct impact on the quality of the code.

I think the reason its not easy replicable is:

1. It takes a ton of initial investment and ongoing maintenance but its worth it when your code base is gigantic.

2. There is a consistent set of top down enforced rules. With the consistency it becomes much, much easier to build tight integrations between tools.

(almost?) everything is buildable by a single build system (blaze). When anyone can consistently build/test/run anything in your codebase it becomes a lot easier to build a whole host of potential tools like code search.

Probably someone can dive deeper than I can. But one thing I learned the most important property for a code base to be maintainable/scalable is consistency.