Canada

There's at least as many parts in a modern reactor as in a dishwasher, but leaving that aside the modular building thing also failed to take off the n times it's been tried, and for similar reasons. I fully believe there's a speedup if you do the same project multiple times, although you'd find it would plateau after a while. There's also a speedup associated with building something large and in place.

The big savings happen when you reach a production run where you can build or configure specialised tooling and run it until after it's earned itself back.