To clarify, I don't think that complex build systems are only used at FAANGs, I think that their usefulness is only realized at FAANGs. From what I've seen at smaller companies, most people are using these tools because everyone else does, not because their software production suffers from the kinds of problems that these tools solve. These tools also seem to provide the mental framework that people need to think about their software production processes, so I guess there's that.