It goes even further than that. Building bigger rocket engines is really hard because turbo-pumps and nozzles don't scale well. Smaller rockets are exponentia

It goes even further than that. Building bigger rocket engines is really hard because turbo-pumps and nozzles don't scale well. Smaller rockets are exponentially cheaper to design and produce. See the RD-170 program for example: it was easier to just use 4 nozzles instead of 1 to achieve the same output.