Many smaller engines is cheaper than one big one as you can streamline manufacturing. Also large engines develop combustion instability much easier. They're als

Many smaller engines is cheaper than one big one as you can streamline manufacturing. Also large engines develop combustion instability much easier. They're also harder to cool because of the square-cube law (more heat, less surface area). It also gives you engine out capability and also the ability to effectively throttle the rocket in a much more fine grained way by shutting off engines.