Google's architecture isn't designed for individual developer productivity. It's a global optimisation. Google appears to value continual evolution of products,

Google's architecture isn't designed for individual developer productivity. It's a global optimisation. Google appears to value continual evolution of products, infrastructure and code, and the monorepo successfully achieves that. In my experience the alternative tends to lead to divergence of codebases and products. We've all seen companies that have some great products counterbalanced with a long tail of products that behave completely differently, or are orphaned, or take decades to move to new infrastructure or integrate with other products.