That, and larger plants. Things like concrete containment vessels have costs relative to the surface area of a hemisphere, while power output scales with the vo

That, and larger plants. Things like concrete containment vessels have costs relative to the surface area of a hemisphere, while power output scales with the volume. But the big driver was economies of scale. Building multiple copies of the same or similar design means you can have longer production runs of steam generators, pressure vessels, turbines, etc.