One reason come to mind: Conway's law. If you have a monolithic team a monolithic server is usually a pretty good solution to a problem. If you have multiple te

One reason come to mind: Conway's law. If you have a monolithic team a monolithic server is usually a pretty good solution to a problem. If you have multiple teams you're likely to wind up with an architecture that lets them work more independently, leading to separate release schedules. ... which perhaps just shifts the question to "why do you need multiple independent teams and not just use a monolithic development team?"