Sure there is. For thousands of classes/functions, I can test the boundaries between them in nanoseconds each. Integration tests are the important part, because with the quality of AI coding these days, unit testing is a waste of time.

With micro services, that same function call is now a minimum of 200us. And now I have LOC for serialization/deserialization, retries, error handling, etc, bloating my code and making it harder to understand, plus now to do the same integration test I need to understand N different build systems for each component.