They aren't built in, it's just that the need for them is impossible to ignore. Developers (and management) can't help but recognize and respect modularity in microservices because the separation of services and the APIs between them make the modularity obvious. When the separation between modules only exists in code, and even then only when seen through the eyes of someone who understands the modular architecture of the codebase, it is easily ignored, inevitably forgotten, and might as well not exist at all.