I guess I'll echo some of the other comments re: extensibility. For us, Bazel's Starlark language is useful because it allows us to integrate w/ non-JS things like protobuf schema definition files. I suspect most companies are going to have hybrid stacks instead of Node.js-only ones. FWIW, Bazel vs Buck have some history wrt adoption wars, and Bazel largely pulled ahead due to a better ability to flourish an ecosystem (hell, the entire JS ecosystem around it is done via the extensibility system). It very much reminds me of how Typescript won against Flow.